class Hash

Parent:
Object
Included modules:
Enumerable

A Hash is a dictionary-like collection of unique keys and their values. Also called associative arrays, they are similar to Arrays, but where an Array uses integers as its index, a Hash allows you to use any object type.

Hashes enumerate their values in the order that the corresponding keys were inserted.

A Hash can be easily created by using its implicit form:

grades = { "Jane Doe" => 10, "Jim Doe" => 6 }

Hashes allow an alternate syntax for keys that are symbols. Instead of

options = { :font_size => 10, :font_family => "Arial" }

You could write it as:

options = { font_size: 10, font_family: "Arial" }

Each named key is a symbol you can access in hash:

options[:font_size]  # => 10

A Hash can also be created through its ::new method:

grades = Hash.new
grades["Dorothy Doe"] = 9

Hashes have a default value that is returned when accessing keys that do not exist in the hash. If no default is set nil is used. You can set the default value by sending it as an argument to Hash.new:

grades = Hash.new(0)

Or by using the default= method:

grades = {"Timmy Doe" => 8}
grades.default = 0

Accessing a value in a Hash requires using its key:

puts grades["Jane Doe"] # => 0

Common Uses

Hashes are an easy way to represent data structures, such as

books         = {}
books[:matz]  = "The Ruby Programming Language"
books[:black] = "The Well-Grounded Rubyist"

Hashes are also commonly used as a way to have named parameters in functions. Note that no brackets are used below. If a hash is the last argument on a method call, no braces are needed, thus creating a really clean interface:

Person.create(name: "John Doe", age: 27)

def self.create(params)
  @name = params[:name]
  @age  = params[:age]
end

Hash Keys

Two objects refer to the same hash key when their hash value is identical and the two objects are eql? to each other.

A user-defined class may be used as a hash key if the hash and eql? methods are overridden to provide meaningful behavior. By default, separate instances refer to separate hash keys.

A typical implementation of hash is based on the object's data while eql? is usually aliased to the overridden == method:

class Book
  attr_reader :author, :title

  def initialize(author, title)
    @author = author
    @title = title
  end

  def ==(other)
    self.class === other and
      other.author == @author and
      other.title == @title
  end

  alias eql? ==

  def hash
    @author.hash ^ @title.hash # XOR
  end
end

book1 = Book.new 'matz', 'Ruby in a Nutshell'
book2 = Book.new 'matz', 'Ruby in a Nutshell'

reviews = {}

reviews[book1] = 'Great reference!'
reviews[book2] = 'Nice and compact!'

reviews.length #=> 1

See also Object#hash and Object#eql?

Public Class Methods

Hash[ key, value, ... ] → new_hash Show source
Hash[ [ [key, value], ... ] ] → new_hash
Hash[ object ] → new_hash 
static VALUE
rb_hash_s_create(int argc, VALUE *argv, VALUE klass)
{
    VALUE hash, tmp;

    if (argc == 1) {
        tmp = rb_hash_s_try_convert(Qnil, argv[0]);
        if (!NIL_P(tmp)) {
            hash = hash_alloc(klass);
            if (RHASH_AR_TABLE_P(tmp)) {
                ar_copy(hash, tmp);
            }
            else {
                RHASH_ST_TABLE_SET(hash, st_copy(RHASH_ST_TABLE(tmp)));
            }
            return hash;
        }

        tmp = rb_check_array_type(argv[0]);
        if (!NIL_P(tmp)) {
            long i;

            hash = hash_alloc(klass);
            for (i = 0; i < RARRAY_LEN(tmp); ++i) {
                VALUE e = RARRAY_AREF(tmp, i);
                VALUE v = rb_check_array_type(e);
                VALUE key, val = Qnil;

                if (NIL_P(v)) {
                    rb_raise(rb_eArgError, "wrong element type %s at %ld (expected array)",
                             rb_builtin_class_name(e), i);
                }
                switch (RARRAY_LEN(v)) {
                  default:
                    rb_raise(rb_eArgError, "invalid number of elements (%ld for 1..2)",
                             RARRAY_LEN(v));
                  case 2:
                    val = RARRAY_AREF(v, 1);
                  case 1:
                    key = RARRAY_AREF(v, 0);
                    rb_hash_aset(hash, key, val);
                }
            }
            return hash;
        }
    }
    if (argc % 2 != 0) {
        rb_raise(rb_eArgError, "odd number of arguments for Hash");
    }

    hash = hash_alloc(klass);
    rb_hash_bulk_insert(argc, argv, hash);
    hash_verify(hash);
    return hash;
}

Creates a new hash populated with the given objects.

Similar to the literal { key => value, ... }. In the first form, keys and values occur in pairs, so there must be an even number of arguments.

The second and third form take a single argument which is either an array of key-value pairs or an object convertible to a hash.

Hash["a", 100, "b", 200]             #=> {"a"=>100, "b"=>200}
Hash[ [ ["a", 100], ["b", 200] ] ]   #=> {"a"=>100, "b"=>200}
Hash["a" => 100, "b" => 200]         #=> {"a"=>100, "b"=>200}
new → new_hash Show source
new(obj) → new_hash
new {|hash, key| block } → new_hash 
static VALUE
rb_hash_initialize(int argc, VALUE *argv, VALUE hash)
{
    VALUE ifnone;

    rb_hash_modify(hash);
    if (rb_block_given_p()) {
        rb_check_arity(argc, 0, 0);
        ifnone = rb_block_proc();
        SET_PROC_DEFAULT(hash, ifnone);
    }
    else {
        rb_check_arity(argc, 0, 1);
        ifnone = argc == 0 ? Qnil : argv[0];
        RHASH_SET_IFNONE(hash, ifnone);
    }

    return hash;
}

Returns a new, empty hash. If this hash is subsequently accessed by a key that doesn't correspond to a hash entry, the value returned depends on the style of new used to create the hash. In the first form, the access returns nil. If obj is specified, this single object will be used for all default values. If a block is specified, it will be called with the hash object and the key, and should return the default value. It is the block's responsibility to store the value in the hash if required.

h = Hash.new("Go Fish")
h["a"] = 100
h["b"] = 200
h["a"]           #=> 100
h["c"]           #=> "Go Fish"
# The following alters the single default object
h["c"].upcase!   #=> "GO FISH"
h["d"]           #=> "GO FISH"
h.keys           #=> ["a", "b"]

# While this creates a new default object each time
h = Hash.new { |hash, key| hash[key] = "Go Fish: #{key}" }
h["c"]           #=> "Go Fish: c"
h["c"].upcase!   #=> "GO FISH: C"
h["d"]           #=> "Go Fish: d"
h.keys           #=> ["c", "d"]
ruby2_keywords_hash(hash) → hash Show source 
static VALUE
rb_hash_s_ruby2_keywords_hash(VALUE dummy, VALUE hash)
{
    Check_Type(hash, T_HASH);
    hash = rb_hash_dup(hash);
    RHASH(hash)->basic.flags |= RHASH_PASS_AS_KEYWORDS;
    return hash;
}

Duplicates a given hash and adds a ruby2_keywords flag. This method is not for casual use; debugging, researching, and some truly necessary cases like deserialization of arguments.

h = {k: 1}
h = Hash.ruby2_keywords_hash(h)
def foo(k: 42)
  k
end
foo(*[h]) #=> 1 with neither a warning or an error
ruby2_keywords_hash?(hash) → true or false Show source 
static VALUE
rb_hash_s_ruby2_keywords_hash_p(VALUE dummy, VALUE hash)
{
    Check_Type(hash, T_HASH);
    return (RHASH(hash)->basic.flags & RHASH_PASS_AS_KEYWORDS) ? Qtrue : Qfalse;
}

Checks if a given hash is flagged by Module#ruby2_keywords (or Proc#ruby2_keywords). This method is not for casual use; debugging, researching, and some truly necessary cases like serialization of arguments.

ruby2_keywords def foo(*args)
  Hash.ruby2_keywords_hash?(args.last)
end
foo(k: 1)   #=> true
foo({k: 1}) #=> false
try_convert(obj) → hash or nil Show source 
static VALUE
rb_hash_s_try_convert(VALUE dummy, VALUE hash)
{
    return rb_check_hash_type(hash);
}

Try to convert obj into a hash, using to_hash method. Returns converted hash or nil if obj cannot be converted for any reason.

Hash.try_convert({1=>2})   # => {1=>2}
Hash.try_convert("1=>2")   # => nil

Public Instance Methods

hash < other → true or false Show source 
static VALUE
rb_hash_lt(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) >= RHASH_SIZE(other)) return Qfalse;
    return hash_le(hash, other);
}

Returns true if hash is subset of other.

h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 < h2    #=> true
h2 < h1    #=> false
h1 < h1    #=> false
hash <= other → true or false Show source 
static VALUE
rb_hash_le(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) > RHASH_SIZE(other)) return Qfalse;
    return hash_le(hash, other);
}

Returns true if hash is subset of other or equals to other.

h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 <= h2   #=> true
h2 <= h1   #=> false
h1 <= h1   #=> true
hsh == other_hash → true or false Show source 
static VALUE
rb_hash_equal(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, FALSE);
}

Equality—Two hashes are equal if they each contain the same number of keys and if each key-value pair is equal to (according to Object#==) the corresponding elements in the other hash.

h1 = { "a" => 1, "c" => 2 }
h2 = { 7 => 35, "c" => 2, "a" => 1 }
h3 = { "a" => 1, "c" => 2, 7 => 35 }
h4 = { "a" => 1, "d" => 2, "f" => 35 }
h1 == h2   #=> false
h2 == h3   #=> true
h3 == h4   #=> false

The orders of each hashes are not compared.

h1 = { "a" => 1, "c" => 2 }
h2 = { "c" => 2, "a" => 1 }
h1 == h2   #=> true
hash > other → true or false Show source 
static VALUE
rb_hash_gt(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) <= RHASH_SIZE(other)) return Qfalse;
    return hash_le(other, hash);
}

Returns true if other is subset of hash.

h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 > h2    #=> false
h2 > h1    #=> true
h1 > h1    #=> false
hash >= other → true or false Show source 
static VALUE
rb_hash_ge(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) < RHASH_SIZE(other)) return Qfalse;
    return hash_le(other, hash);
}

Returns true if other is subset of hash or equals to hash.

h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 >= h2   #=> false
h2 >= h1   #=> true
h1 >= h1   #=> true
hsh[key] → value Show source 
VALUE
rb_hash_aref(VALUE hash, VALUE key)
{
    st_data_t val;

    if (hash_stlike_lookup(hash, key, &val)) {
        return (VALUE)val;
    }
    else {
        return rb_hash_default_value(hash, key);
    }
}

Element Reference—Retrieves the value object corresponding to the key object. If not found, returns the default value (see Hash::new for details).

h = { "a" => 100, "b" => 200 }
h["a"]   #=> 100
h["c"]   #=> nil
hsh[key] = value → value Show source 
VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
    int iter_lev = RHASH_ITER_LEV(hash);

    rb_hash_modify(hash);

    if (RHASH_TABLE_NULL_P(hash)) {
        if (iter_lev > 0) no_new_key();
        ar_alloc_table(hash);
    }

    if (RHASH_TYPE(hash) == &identhash || rb_obj_class(key) != rb_cString) {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset, val);
    }
    else {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset_str, val);
    }
    return val;
}

Element Assignment

Associates the value given by value with the key given by key.

h = { "a" => 100, "b" => 200 }
h["a"] = 9
h["c"] = 4
h   #=> {"a"=>9, "b"=>200, "c"=>4}
h.store("d", 42) #=> 42
h   #=> {"a"=>9, "b"=>200, "c"=>4, "d"=>42}

key should not have its value changed while it is in use as a key (an unfrozen String passed as a key will be duplicated and frozen).

a = "a"
b = "b".freeze
h = { a => 100, b => 200 }
h.key(100).equal? a #=> false
h.key(200).equal? b #=> true
any? [{ |(key, value)| block }] → true or false Show source
any?(pattern) → true or false 
static VALUE
rb_hash_any_p(int argc, VALUE *argv, VALUE hash)
{
    VALUE args[2];
    args[0] = Qfalse;

    rb_check_arity(argc, 0, 1);
    if (RHASH_EMPTY_P(hash)) return Qfalse;
    if (argc) {
        if (rb_block_given_p()) {
            rb_warn("given block not used");
        }
        args[1] = argv[0];

        rb_hash_foreach(hash, any_p_i_pattern, (VALUE)args);
    }
    else {
        if (!rb_block_given_p()) {
            /* yields pairs, never false */
            return Qtrue;
        }
        if (rb_block_arity() > 1)
            rb_hash_foreach(hash, any_p_i_fast, (VALUE)args);
        else
            rb_hash_foreach(hash, any_p_i, (VALUE)args);
    }
    return args[0];
}

See also Enumerable#any?

assoc(obj) → an_array or nil Show source 
VALUE
rb_hash_assoc(VALUE hash, VALUE key)
{
    st_table *table;
    const struct st_hash_type *orighash;
    VALUE args[2];

    if (RHASH_EMPTY_P(hash)) return Qnil;

    ar_force_convert_table(hash, __FILE__, __LINE__);
    HASH_ASSERT(RHASH_ST_TABLE_P(hash));
    table = RHASH_ST_TABLE(hash);
    orighash = table->type;

    if (orighash != &identhash) {
        VALUE value;
        struct reset_hash_type_arg ensure_arg;
        struct st_hash_type assochash;

        assochash.compare = assoc_cmp;
        assochash.hash = orighash->hash;
        table->type = &assochash;
        args[0] = hash;
        args[1] = key;
        ensure_arg.hash = hash;
        ensure_arg.orighash = orighash;
        value = rb_ensure(lookup2_call, (VALUE)&args, reset_hash_type, (VALUE)&ensure_arg);
        if (value != Qundef) return rb_assoc_new(key, value);
    }

    args[0] = key;
    args[1] = Qnil;
    rb_hash_foreach(hash, assoc_i, (VALUE)args);
    return args[1];
}

Searches through the hash comparing obj with the key using ==. Returns the key-value pair (two elements array) or nil if no match is found. See Array#assoc.

h = {"colors"  => ["red", "blue", "green"],
     "letters" => ["a", "b", "c" ]}
h.assoc("letters")  #=> ["letters", ["a", "b", "c"]]
h.assoc("foo")      #=> nil
clear → hsh Show source 
VALUE
rb_hash_clear(VALUE hash)
{
    rb_hash_modify_check(hash);

    if (RHASH_ITER_LEV(hash) > 0) {
        rb_hash_foreach(hash, clear_i, 0);
    }
    else if (RHASH_AR_TABLE_P(hash)) {
        ar_clear(hash);
    }
    else {
        st_clear(RHASH_ST_TABLE(hash));
    }

    return hash;
}

Removes all key-value pairs from hsh.

h = { "a" => 100, "b" => 200 }   #=> {"a"=>100, "b"=>200}
h.clear                          #=> {}
compact → new_hash Show source 
static VALUE
rb_hash_compact(VALUE hash)
{
    VALUE result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_foreach(hash, set_if_not_nil, result);
    }
    return result;
}

Returns a new hash with the nil values/key pairs removed

h = { a: 1, b: false, c: nil }
h.compact     #=> { a: 1, b: false }
h             #=> { a: 1, b: false, c: nil }
compact! → hsh or nil Show source 
static VALUE
rb_hash_compact_bang(VALUE hash)
{
    st_index_t n;
    rb_hash_modify_check(hash);
    n = RHASH_SIZE(hash);
    if (n) {
        rb_hash_foreach(hash, delete_if_nil, hash);
        if (n != RHASH_SIZE(hash))
            return hash;
    }
    return Qnil;
}

Removes all nil values from the hash. Returns nil if no changes were made, otherwise returns the hash.

h = { a: 1, b: false, c: nil }
h.compact!     #=> { a: 1, b: false }
compare_by_identity → hsh Show source 
static VALUE
rb_hash_compare_by_id(VALUE hash)
{
    VALUE tmp;
    st_table *identtable;

    if (rb_hash_compare_by_id_p(hash)) return hash;

    rb_hash_modify_check(hash);
    ar_force_convert_table(hash, __FILE__, __LINE__);
    HASH_ASSERT(RHASH_ST_TABLE_P(hash));

    tmp = hash_alloc(0);
    identtable = rb_init_identtable_with_size(RHASH_SIZE(hash));
    RHASH_ST_TABLE_SET(tmp, identtable);
    rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
    st_free_table(RHASH_ST_TABLE(hash));
    RHASH_ST_TABLE_SET(hash, identtable);
    RHASH_ST_CLEAR(tmp);
    rb_gc_force_recycle(tmp);

    return hash;
}

Makes hsh compare its keys by their identity, i.e. it will consider exact same objects as same keys.

h1 = { "a" => 100, "b" => 200, :c => "c" }
h1["a"]        #=> 100
h1.compare_by_identity
h1.compare_by_identity? #=> true
h1["a".dup]    #=> nil  # different objects.
h1[:c]         #=> "c"  # same symbols are all same.
compare_by_identity? → true or false Show source 
MJIT_FUNC_EXPORTED VALUE
rb_hash_compare_by_id_p(VALUE hash)
{
    if (RHASH_ST_TABLE_P(hash) && RHASH_ST_TABLE(hash)->type == &identhash) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}

Returns true if hsh will compare its keys by their identity. Also see Hash#compare_by_identity.

deconstruct_keys(p1) Show source 
static VALUE
rb_hash_deconstruct_keys(VALUE hash, VALUE keys)
{
    return hash;
}
default(key=nil) → obj Show source 
static VALUE
rb_hash_default(int argc, VALUE *argv, VALUE hash)
{
    VALUE args[2], ifnone;

    rb_check_arity(argc, 0, 1);
    ifnone = RHASH_IFNONE(hash);
    if (FL_TEST(hash, RHASH_PROC_DEFAULT)) {
        if (argc == 0) return Qnil;
        args[0] = hash;
        args[1] = argv[0];
        return rb_funcallv(ifnone, id_yield, 2, args);
    }
    return ifnone;
}

Returns the default value, the value that would be returned by hsh if key did not exist in hsh. See also Hash::new and Hash#default=.

h = Hash.new                            #=> {}
h.default                               #=> nil
h.default(2)                            #=> nil

h = Hash.new("cat")                     #=> {}
h.default                               #=> "cat"
h.default(2)                            #=> "cat"

h = Hash.new {|h,k| h[k] = k.to_i*10}   #=> {}
h.default                               #=> nil
h.default(2)                            #=> 20
default = obj → obj Show source 
static VALUE
rb_hash_set_default(VALUE hash, VALUE ifnone)
{
    rb_hash_modify_check(hash);
    SET_DEFAULT(hash, ifnone);
    return ifnone;
}

Sets the default value, the value returned for a key that does not exist in the hash. It is not possible to set the default to a Proc that will be executed on each key lookup.

h = { "a" => 100, "b" => 200 }
h.default = "Go fish"
h["a"]     #=> 100
h["z"]     #=> "Go fish"
# This doesn't do what you might hope...
h.default = proc do |hash, key|
  hash[key] = key + key
end
h[2]       #=> #<Proc:0x401b3948@-:6>
h["cat"]   #=> #<Proc:0x401b3948@-:6>
default_proc → anObject Show source 
static VALUE
rb_hash_default_proc(VALUE hash)
{
    if (FL_TEST(hash, RHASH_PROC_DEFAULT)) {
        return RHASH_IFNONE(hash);
    }
    return Qnil;
}

If Hash::new was invoked with a block, return that block, otherwise return nil.

h = Hash.new {|h,k| h[k] = k*k }   #=> {}
p = h.default_proc                 #=> #<Proc:0x401b3d08@-:1>
a = []                             #=> []
p.call(a, 2)
a                                  #=> [nil, nil, 4]
default_proc = proc_obj or nil Show source 
VALUE
rb_hash_set_default_proc(VALUE hash, VALUE proc)
{
    VALUE b;

    rb_hash_modify_check(hash);
    if (NIL_P(proc)) {
        SET_DEFAULT(hash, proc);
        return proc;
    }
    b = rb_check_convert_type_with_id(proc, T_DATA, "Proc", idTo_proc);
    if (NIL_P(b) || !rb_obj_is_proc(b)) {
        rb_raise(rb_eTypeError,
                 "wrong default_proc type %s (expected Proc)",
                 rb_obj_classname(proc));
    }
    proc = b;
    SET_PROC_DEFAULT(hash, proc);
    return proc;
}

Sets the default proc to be executed on each failed key lookup.

h.default_proc = proc do |hash, key|
  hash[key] = key + key
end
h[2]       #=> 4
h["cat"]   #=> "catcat"
delete(key) → value Show source
delete(key) {| key | block } → value 
static VALUE
rb_hash_delete_m(VALUE hash, VALUE key)
{
    VALUE val;

    rb_hash_modify_check(hash);
    val = rb_hash_delete_entry(hash, key);

    if (val != Qundef) {
        return val;
    }
    else {
        if (rb_block_given_p()) {
            return rb_yield(key);
        }
        else {
            return Qnil;
        }
    }
}

Deletes the key-value pair and returns the value from hsh whose key is equal to key. If the key is not found, it returns nil. If the optional code block is given and the key is not found, pass in the key and return the result of block.

h = { "a" => 100, "b" => 200 }
h.delete("a")                              #=> 100
h.delete("z")                              #=> nil
h.delete("z") { |el| "#{el} not found" }   #=> "z not found"
delete_if {| key, value | block } → hsh Show source
delete_if → an_enumerator 
VALUE
rb_hash_delete_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_foreach(hash, delete_if_i, hash);
    }
    return hash;
}

Deletes every key-value pair from hsh for which block evaluates to true.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.delete_if {|key, value| key >= "b" }   #=> {"a"=>100}
dig(key, ...) → object Show source 
static VALUE
rb_hash_dig(int argc, VALUE *argv, VALUE self)
{
    rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
    self = rb_hash_aref(self, *argv);
    if (!--argc) return self;
    ++argv;
    return rb_obj_dig(argc, argv, self, Qnil);
}

Extracts the nested value specified by the sequence of key objects by calling dig at each step, returning nil if any intermediate step is nil.

h = { foo: {bar: {baz: 1}}}

h.dig(:foo, :bar, :baz)     #=> 1
h.dig(:foo, :zot, :xyz)     #=> nil

g = { foo: [10, 11, 12] }
g.dig(:foo, 1)              #=> 11
g.dig(:foo, 1, 0)           #=> TypeError: Integer does not have #dig method
g.dig(:foo, :bar)           #=> TypeError: no implicit conversion of Symbol into Integer
each {| key, value | block } → hsh Show source
each_pair {| key, value | block } → hsh
each → an_enumerator
each_pair → an_enumerator 
static VALUE
rb_hash_each_pair(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    if (rb_block_arity() > 1)
        rb_hash_foreach(hash, each_pair_i_fast, 0);
    else
        rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}

Calls block once for each key in hsh, passing the key-value pair as parameters.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each {|key, value| puts "#{key} is #{value}" }

produces:

a is 100
b is 200
each_key {| key | block } → hsh Show source
each_key → an_enumerator 
static VALUE
rb_hash_each_key(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_foreach(hash, each_key_i, 0);
    return hash;
}

Calls block once for each key in hsh, passing the key as a parameter.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each_key {|key| puts key }

produces:

a
b
each_pair {| key, value | block } → hsh Show source
each_pair → an_enumerator 
static VALUE
rb_hash_each_pair(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    if (rb_block_arity() > 1)
        rb_hash_foreach(hash, each_pair_i_fast, 0);
    else
        rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}

Calls block once for each key in hsh, passing the key-value pair as parameters.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each {|key, value| puts "#{key} is #{value}" }

produces:

a is 100
b is 200
each_value {| value | block } → hsh Show source
each_value → an_enumerator 
static VALUE
rb_hash_each_value(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_foreach(hash, each_value_i, 0);
    return hash;
}

Calls block once for each key in hsh, passing the value as a parameter.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each_value {|value| puts value }

produces:

100
200
empty? → true or false Show source 
static VALUE
rb_hash_empty_p(VALUE hash)
{
    return RHASH_EMPTY_P(hash) ? Qtrue : Qfalse;
}

Returns true if hsh contains no key-value pairs.

{}.empty?   #=> true
eql?(other) → true or false Show source 
static VALUE
rb_hash_eql(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, TRUE);
}

Returns true if hash and other are both hashes with the same content. The orders of each hashes are not compared.

fetch(key [, default] ) → obj Show source
fetch(key) {| key | block } → obj 
static VALUE
rb_hash_fetch_m(int argc, VALUE *argv, VALUE hash)
{
    VALUE key;
    st_data_t val;
    long block_given;

    rb_check_arity(argc, 1, 2);
    key = argv[0];

    block_given = rb_block_given_p();
    if (block_given && argc == 2) {
        rb_warn("block supersedes default value argument");
    }

    if (hash_stlike_lookup(hash, key, &val)) {
        return (VALUE)val;
    }
    else {
        if (block_given) {
            return rb_yield(key);
        }
        else if (argc == 1) {
            VALUE desc = rb_protect(rb_inspect, key, 0);
            if (NIL_P(desc)) {
                desc = rb_any_to_s(key);
            }
            desc = rb_str_ellipsize(desc, 65);
            rb_key_err_raise(rb_sprintf("key not found: %"PRIsVALUE, desc), hash, key);
        }
        else {
            return argv[1];
        }
    }
}

Returns a value from the hash for the given key. If the key can't be found, there are several options: With no other arguments, it will raise a KeyError exception; if default is given, then that will be returned; if the optional code block is specified, then that will be run and its result returned.

h = { "a" => 100, "b" => 200 }
h.fetch("a")                            #=> 100
h.fetch("z", "go fish")                 #=> "go fish"
h.fetch("z") { |el| "go fish, #{el}"}   #=> "go fish, z"

The following example shows that an exception is raised if the key is not found and a default value is not supplied.

h = { "a" => 100, "b" => 200 }
h.fetch("z")

produces:

prog.rb:2:in `fetch': key not found (KeyError)
 from prog.rb:2
fetch_values(key, ...) → array Show source
fetch_values(key, ...) { |key| block } → array 
VALUE
rb_hash_fetch_values(int argc, VALUE *argv, VALUE hash)
{
    VALUE result = rb_ary_new2(argc);
    long i;

    for (i=0; i<argc; i++) {
        rb_ary_push(result, rb_hash_fetch(hash, argv[i]));
    }
    return result;
}

Returns an array containing the values associated with the given keys but also raises KeyError when one of keys can't be found. Also see Hash#values_at and Hash#fetch.

h = { "cat" => "feline", "dog" => "canine", "cow" => "bovine" }

h.fetch_values("cow", "cat")                   #=> ["bovine", "feline"]
h.fetch_values("cow", "bird")                  # raises KeyError
h.fetch_values("cow", "bird") { |k| k.upcase } #=> ["bovine", "BIRD"]
filter {|key, value| block} → a_hash Show source
filter → an_enumerator 
VALUE
rb_hash_select(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_foreach(hash, select_i, result);
    }
    return result;
}

Returns a new hash consisting of entries for which the block returns true.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.select {|k,v| k > "a"}  #=> {"b" => 200, "c" => 300}
h.select {|k,v| v < 200}  #=> {"a" => 100}

Hash#filter is an alias for Hash#select.

filter! {| key, value | block } → hsh or nil Show source
filter! → an_enumerator 
VALUE
rb_hash_select_bang(VALUE hash)
{
    st_index_t n;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    n = RHASH_SIZE(hash);
    if (!n) return Qnil;
    rb_hash_foreach(hash, keep_if_i, hash);
    if (n == RHASH_SIZE(hash)) return Qnil;
    return hash;
}

Equivalent to Hash#keep_if, but returns nil if no changes were made.

Hash#filter! is an alias for Hash#select!.

flatten → an_array Show source
flatten(level) → an_array 
static VALUE
rb_hash_flatten(int argc, VALUE *argv, VALUE hash)
{
    VALUE ary;

    rb_check_arity(argc, 0, 1);

    if (argc) {
        int level = NUM2INT(argv[0]);

        if (level == 0) return rb_hash_to_a(hash);

        ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
        rb_hash_foreach(hash, flatten_i, ary);
        level--;

        if (level > 0) {
            VALUE ary_flatten_level = INT2FIX(level);
            rb_funcallv(ary, id_flatten_bang, 1, &ary_flatten_level);
        }
        else if (level < 0) {
            /* flatten recursively */
            rb_funcallv(ary, id_flatten_bang, 0, 0);
        }
    }
    else {
        ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
        rb_hash_foreach(hash, flatten_i, ary);
    }

    return ary;
}

Returns a new array that is a one-dimensional flattening of this hash. That is, for every key or value that is an array, extract its elements into the new array. Unlike Array#flatten, this method does not flatten recursively by default. The optional level argument determines the level of recursion to flatten.

a =  {1=> "one", 2 => [2,"two"], 3 => "three"}
a.flatten    # => [1, "one", 2, [2, "two"], 3, "three"]
a.flatten(2) # => [1, "one", 2, 2, "two", 3, "three"]
has_key?(key) → true or false Show source 
MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

Note that include? and member? do not test member equality using == as do other Enumerables.

See also Enumerable#include?

has_value?(value) → true or false Show source 
static VALUE
rb_hash_has_value(VALUE hash, VALUE val)
{
    VALUE data[2];

    data[0] = Qfalse;
    data[1] = val;
    rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
    return data[0];
}

Returns true if the given value is present for some key in hsh.

h = { "a" => 100, "b" => 200 }
h.value?(100)   #=> true
h.value?(999)   #=> false
hash → integer Show source 
static VALUE
rb_hash_hash(VALUE hash)
{
    st_index_t size = RHASH_SIZE(hash);
    st_index_t hval = rb_hash_start(size);
    hval = rb_hash_uint(hval, (st_index_t)rb_hash_hash);
    if (size) {
        rb_hash_foreach(hash, hash_i, (VALUE)&hval);
    }
    hval = rb_hash_end(hval);
    return ST2FIX(hval);
}

Compute a hash-code for this hash. Two hashes with the same content will have the same hash code (and will compare using eql?).

See also Object#hash.

include?(key) → true or false Show source 
MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

Note that include? and member? do not test member equality using == as do other Enumerables.

See also Enumerable#include?

replace(other_hash) → hsh Show source 
static VALUE
rb_hash_replace(VALUE hash, VALUE hash2)
{
    rb_hash_modify_check(hash);
    if (hash == hash2) return hash;
    if (RHASH_ITER_LEV(hash) > 0) {
        rb_raise(rb_eRuntimeError, "can't replace hash during iteration");
    }
    hash2 = to_hash(hash2);

    COPY_DEFAULT(hash, hash2);

    if (RHASH_AR_TABLE_P(hash)) {
        if (RHASH_AR_TABLE_P(hash2)) {
            ar_clear(hash);
        }
        else {
            ar_free_and_clear_table(hash);
            RHASH_ST_TABLE_SET(hash, st_init_table_with_size(RHASH_TYPE(hash2), RHASH_SIZE(hash2)));
        }
    }
    else {
        if (RHASH_AR_TABLE_P(hash2)) {
            st_free_table(RHASH_ST_TABLE(hash));
            RHASH_ST_CLEAR(hash);
        }
        else {
            st_clear(RHASH_ST_TABLE(hash));
            RHASH_TBL_RAW(hash)->type = RHASH_ST_TABLE(hash2)->type;
        }
    }
    rb_hash_foreach(hash2, rb_hash_rehash_i, (VALUE)hash);

    rb_gc_writebarrier_remember(hash);

    return hash;
}

Replaces the contents of hsh with the contents of other_hash.

h = { "a" => 100, "b" => 200 }
h.replace({ "c" => 300, "d" => 400 })   #=> {"c"=>300, "d"=>400}
to_s → string Show source
inspect → string 
static VALUE
rb_hash_inspect(VALUE hash)
{
    if (RHASH_EMPTY_P(hash))
        return rb_usascii_str_new2("{}");
    return rb_exec_recursive(inspect_hash, hash, 0);
}

Return the contents of this hash as a string.

h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300  }
h.to_s   #=> "{\"c\"=>300, \"a\"=>100, \"d\"=>400}"
Also aliased as: to_s
invert → new_hash Show source 
static VALUE
rb_hash_invert(VALUE hash)
{
    VALUE h = rb_hash_new_with_size(RHASH_SIZE(hash));

    rb_hash_foreach(hash, rb_hash_invert_i, h);
    return h;
}

Returns a new hash created by using hsh's values as keys, and the keys as values. If a key with the same value already exists in the hsh, then the last one defined will be used, the earlier value(s) will be discarded.

h = { "n" => 100, "m" => 100, "y" => 300, "d" => 200, "a" => 0 }
h.invert   #=> {0=>"a", 100=>"m", 200=>"d", 300=>"y"}

If there is no key with the same value, Hash#invert is involutive.

h = { a: 1, b: 3, c: 4 }
h.invert.invert == h #=> true

The condition, no key with the same value, can be tested by comparing the size of inverted hash.

# no key with the same value
h = { a: 1, b: 3, c: 4 }
h.size == h.invert.size #=> true

# two (or more) keys has the same value
h = { a: 1, b: 3, c: 1 }
h.size == h.invert.size #=> false
keep_if {| key, value | block } → hsh Show source
keep_if → an_enumerator 
VALUE
rb_hash_keep_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_foreach(hash, keep_if_i, hash);
    }
    return hash;
}

Deletes every key-value pair from hsh for which block evaluates to false.

If no block is given, an enumerator is returned instead.

See also Hash#select!.

key(value) → key Show source 
static VALUE
rb_hash_key(VALUE hash, VALUE value)
{
    VALUE args[2];

    args[0] = value;
    args[1] = Qnil;

    rb_hash_foreach(hash, key_i, (VALUE)args);

    return args[1];
}

Returns the key of an occurrence of a given value. If the value is not found, returns nil.

h = { "a" => 100, "b" => 200, "c" => 300, "d" => 300 }
h.key(200)   #=> "b"
h.key(300)   #=> "c"
h.key(999)   #=> nil
key?(key) → true or false Show source 
MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

Note that include? and member? do not test member equality using == as do other Enumerables.

See also Enumerable#include?

keys → array Show source 
MJIT_FUNC_EXPORTED VALUE
rb_hash_keys(VALUE hash)
{
    st_index_t size = RHASH_SIZE(hash);
    VALUE keys =  rb_ary_new_capa(size);

    if (size == 0) return keys;

    if (ST_DATA_COMPATIBLE_P(VALUE)) {
        RARRAY_PTR_USE_TRANSIENT(keys, ptr, {
            if (RHASH_AR_TABLE_P(hash)) {
                size = ar_keys(hash, ptr, size);
            }
            else {
                st_table *table = RHASH_ST_TABLE(hash);
                size = st_keys(table, ptr, size);
            }
        });
        rb_gc_writebarrier_remember(keys);
        rb_ary_set_len(keys, size);
    }
    else {
        rb_hash_foreach(hash, keys_i, keys);
    }

    return keys;
}

Returns a new array populated with the keys from this hash. See also Hash#values.

h = { "a" => 100, "b" => 200, "c" => 300, "d" => 400 }
h.keys   #=> ["a", "b", "c", "d"]
length → integer Show source 
VALUE
rb_hash_size(VALUE hash)
{
    return INT2FIX(RHASH_SIZE(hash));
}

Returns the number of key-value pairs in the hash.

h = { "d" => 100, "a" => 200, "v" => 300, "e" => 400 }
h.size          #=> 4
h.delete("a")   #=> 200
h.size          #=> 3
h.length        #=> 3

Hash#length is an alias for Hash#size.

member?(key) → true or false Show source 
MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

Note that include? and member? do not test member equality using == as do other Enumerables.

See also Enumerable#include?

merge(other_hash1, other_hash2, ...) → new_hash Show source
merge(other_hash1, other_hash2, ...) {|key, oldval, newval| block}
→ new_hash 
static VALUE
rb_hash_merge(int argc, VALUE *argv, VALUE self)
{
    return rb_hash_update(argc, argv, rb_hash_dup(self));
}

Returns a new hash that combines the contents of the receiver and the contents of the given hashes.

If no block is given, entries with duplicate keys are overwritten with the values from each other_hash successively, otherwise the value for each duplicate key is determined by calling the block with the key, its value in the receiver and its value in each other_hash.

When called without any argument, returns a copy of the receiver.

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge          #=> {"a"=>100, "b"=>200}
h1.merge(h2)      #=> {"a"=>100, "b"=>246, "c"=>300}
h1.merge(h2, h3)  #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}
h1.merge(h2) {|key, oldval, newval| newval - oldval}
                  #=> {"a"=>100, "b"=>46,  "c"=>300}
h1.merge(h2, h3) {|key, oldval, newval| newval - oldval}
                  #=> {"a"=>100, "b"=>311, "c"=>300, "d"=>400}
h1                #=> {"a"=>100, "b"=>200}
merge!(other_hash1, other_hash2, ...) → hsh Show source
merge!(other_hash1, other_hash2, ...) {|key, oldval, newval| block} 
static VALUE
rb_hash_update(int argc, VALUE *argv, VALUE self)
{
    int i;
    bool block_given = rb_block_given_p();

    rb_hash_modify(self);
    for (i = 0; i < argc; i++){
       VALUE hash = to_hash(argv[i]);
       if (block_given) {
           rb_hash_foreach(hash, rb_hash_update_block_i, self);
       }
       else {
           rb_hash_foreach(hash, rb_hash_update_i, self);
       }
    }
    return self;
}

Adds the contents of the given hashes to the receiver.

If no block is given, entries with duplicate keys are overwritten with the values from each other_hash successively, otherwise the value for each duplicate key is determined by calling the block with the key, its value in the receiver and its value in each other_hash.

h1 = { "a" => 100, "b" => 200 }
h1.merge!          #=> {"a"=>100, "b"=>200}
h1                 #=> {"a"=>100, "b"=>200}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h1.merge!(h2)      #=> {"a"=>100, "b"=>246, "c"=>300}
h1                 #=> {"a"=>100, "b"=>246, "c"=>300}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3)
                   #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}
h1                 #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3) {|key, v1, v2| v1 }
                   #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}
h1                 #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}

Hash#update is an alias for Hash#merge!.

rassoc(obj) → an_array or nil Show source 
VALUE
rb_hash_rassoc(VALUE hash, VALUE obj)
{
    VALUE args[2];

    args[0] = obj;
    args[1] = Qnil;
    rb_hash_foreach(hash, rassoc_i, (VALUE)args);
    return args[1];
}

Searches through the hash comparing obj with the value using ==. Returns the first key-value pair (two-element array) that matches. See also Array#rassoc.

a = {1=> "one", 2 => "two", 3 => "three", "ii" => "two"}
a.rassoc("two")    #=> [2, "two"]
a.rassoc("four")   #=> nil
rehash → hsh Show source 
VALUE
rb_hash_rehash(VALUE hash)
{
    VALUE tmp;
    st_table *tbl;

    if (RHASH_ITER_LEV(hash) > 0) {
        rb_raise(rb_eRuntimeError, "rehash during iteration");
    }
    rb_hash_modify_check(hash);
    if (RHASH_AR_TABLE_P(hash)) {
        tmp = hash_alloc(0);
        ar_alloc_table(tmp);
        rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
        ar_free_and_clear_table(hash);
        ar_copy(hash, tmp);
        ar_free_and_clear_table(tmp);
    }
    else if (RHASH_ST_TABLE_P(hash)) {
        st_table *old_tab = RHASH_ST_TABLE(hash);
        tmp = hash_alloc(0);
        tbl = st_init_table_with_size(old_tab->type, old_tab->num_entries);
        RHASH_ST_TABLE_SET(tmp, tbl);
        rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
        st_free_table(old_tab);
        RHASH_ST_TABLE_SET(hash, tbl);
        RHASH_ST_CLEAR(tmp);
    }
    hash_verify(hash);
    return hash;
}

Rebuilds the hash based on the current hash values for each key. If values of key objects have changed since they were inserted, this method will reindex hsh. If Hash#rehash is called while an iterator is traversing the hash, a RuntimeError will be raised in the iterator.

a = [ "a", "b" ]
c = [ "c", "d" ]
h = { a => 100, c => 300 }
h[a]       #=> 100
a[0] = "z"
h[a]       #=> nil
h.rehash   #=> {["z", "b"]=>100, ["c", "d"]=>300}
h[a]       #=> 100
reject {|key, value| block} → a_hash Show source
reject → an_enumerator 
VALUE
rb_hash_reject(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    if (RTEST(ruby_verbose)) {
        VALUE klass;
        if (HAS_EXTRA_STATES(hash, klass)) {
            rb_warn("extra states are no longer copied: %+"PRIsVALUE, hash);
        }
    }
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_foreach(hash, reject_i, result);
    }
    return result;
}

Returns a new hash consisting of entries for which the block returns false.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.reject {|k,v| k < "b"}  #=> {"b" => 200, "c" => 300}
h.reject {|k,v| v > 100}  #=> {"a" => 100}
reject! {| key, value | block } → hsh or nil Show source
reject! → an_enumerator 
VALUE
rb_hash_reject_bang(VALUE hash)
{
    st_index_t n;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify(hash);
    n = RHASH_SIZE(hash);
    if (!n) return Qnil;
    rb_hash_foreach(hash, delete_if_i, hash);
    if (n == RHASH_SIZE(hash)) return Qnil;
    return hash;
}

Equivalent to Hash#delete_if, but returns nil if no changes were made.

replace(other_hash) → hsh Show source 
static VALUE
rb_hash_replace(VALUE hash, VALUE hash2)
{
    rb_hash_modify_check(hash);
    if (hash == hash2) return hash;
    if (RHASH_ITER_LEV(hash) > 0) {
        rb_raise(rb_eRuntimeError, "can't replace hash during iteration");
    }
    hash2 = to_hash(hash2);

    COPY_DEFAULT(hash, hash2);

    if (RHASH_AR_TABLE_P(hash)) {
        if (RHASH_AR_TABLE_P(hash2)) {
            ar_clear(hash);
        }
        else {
            ar_free_and_clear_table(hash);
            RHASH_ST_TABLE_SET(hash, st_init_table_with_size(RHASH_TYPE(hash2), RHASH_SIZE(hash2)));
        }
    }
    else {
        if (RHASH_AR_TABLE_P(hash2)) {
            st_free_table(RHASH_ST_TABLE(hash));
            RHASH_ST_CLEAR(hash);
        }
        else {
            st_clear(RHASH_ST_TABLE(hash));
            RHASH_TBL_RAW(hash)->type = RHASH_ST_TABLE(hash2)->type;
        }
    }
    rb_hash_foreach(hash2, rb_hash_rehash_i, (VALUE)hash);

    rb_gc_writebarrier_remember(hash);

    return hash;
}

Replaces the contents of hsh with the contents of other_hash.

h = { "a" => 100, "b" => 200 }
h.replace({ "c" => 300, "d" => 400 })   #=> {"c"=>300, "d"=>400}
select {|key, value| block} → a_hash Show source
select → an_enumerator 
VALUE
rb_hash_select(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_foreach(hash, select_i, result);
    }
    return result;
}

Returns a new hash consisting of entries for which the block returns true.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.select {|k,v| k > "a"}  #=> {"b" => 200, "c" => 300}
h.select {|k,v| v < 200}  #=> {"a" => 100}

Hash#filter is an alias for Hash#select.

select! {| key, value | block } → hsh or nil Show source
select! → an_enumerator 
VALUE
rb_hash_select_bang(VALUE hash)
{
    st_index_t n;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    n = RHASH_SIZE(hash);
    if (!n) return Qnil;
    rb_hash_foreach(hash, keep_if_i, hash);
    if (n == RHASH_SIZE(hash)) return Qnil;
    return hash;
}

Equivalent to Hash#keep_if, but returns nil if no changes were made.

Hash#filter! is an alias for Hash#select!.

shift → anArray or obj Show source 
static VALUE
rb_hash_shift(VALUE hash)
{
    struct shift_var var;

    rb_hash_modify_check(hash);
    if (RHASH_AR_TABLE_P(hash)) {
        var.key = Qundef;
        if (RHASH_ITER_LEV(hash) == 0) {
            if (ar_shift(hash, &var.key, &var.val)) {
                return rb_assoc_new(var.key, var.val);
            }
        }
        else {
            rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
            if (var.key != Qundef) {
                rb_hash_delete_entry(hash, var.key);
                return rb_assoc_new(var.key, var.val);
            }
        }
    }
    if (RHASH_ST_TABLE_P(hash)) {
        var.key = Qundef;
        if (RHASH_ITER_LEV(hash) == 0) {
            if (st_shift(RHASH_ST_TABLE(hash), &var.key, &var.val)) {
                return rb_assoc_new(var.key, var.val);
            }
        }
        else {
            rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
            if (var.key != Qundef) {
                rb_hash_delete_entry(hash, var.key);
                return rb_assoc_new(var.key, var.val);
            }
        }
    }
    return rb_hash_default_value(hash, Qnil);
}

Removes a key-value pair from hsh and returns it as the two-item array [ key, value ], or the hash's default value if the hash is empty.

h = { 1 => "a", 2 => "b", 3 => "c" }
h.shift   #=> [1, "a"]
h         #=> {2=>"b", 3=>"c"}
size → integer Show source 
VALUE
rb_hash_size(VALUE hash)
{
    return INT2FIX(RHASH_SIZE(hash));
}

Returns the number of key-value pairs in the hash.

h = { "d" => 100, "a" => 200, "v" => 300, "e" => 400 }
h.size          #=> 4
h.delete("a")   #=> 200
h.size          #=> 3
h.length        #=> 3

Hash#length is an alias for Hash#size.

slice(*keys) → a_hash Show source 
static VALUE
rb_hash_slice(int argc, VALUE *argv, VALUE hash)
{
    int i;
    VALUE key, value, result;

    if (argc == 0 || RHASH_EMPTY_P(hash)) {
        return rb_hash_new();
    }
    result = rb_hash_new_with_size(argc);

    for (i = 0; i < argc; i++) {
        key = argv[i];
        value = rb_hash_lookup2(hash, key, Qundef);
        if (value != Qundef)
            rb_hash_aset(result, key, value);
    }

    return result;
}

Returns a hash containing only the given keys and their values.

h = { a: 100, b: 200, c: 300 }
h.slice(:a)           #=> {:a=>100}
h.slice(:b, :c, :d)   #=> {:b=>200, :c=>300}
store(key, value) → value Show source 
VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
    int iter_lev = RHASH_ITER_LEV(hash);

    rb_hash_modify(hash);

    if (RHASH_TABLE_NULL_P(hash)) {
        if (iter_lev > 0) no_new_key();
        ar_alloc_table(hash);
    }

    if (RHASH_TYPE(hash) == &identhash || rb_obj_class(key) != rb_cString) {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset, val);
    }
    else {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset_str, val);
    }
    return val;
}

Element Assignment

Associates the value given by value with the key given by key.

h = { "a" => 100, "b" => 200 }
h["a"] = 9
h["c"] = 4
h   #=> {"a"=>9, "b"=>200, "c"=>4}
h.store("d", 42) #=> 42
h   #=> {"a"=>9, "b"=>200, "c"=>4, "d"=>42}

key should not have its value changed while it is in use as a key (an unfrozen String passed as a key will be duplicated and frozen).

a = "a"
b = "b".freeze
h = { a => 100, b => 200 }
h.key(100).equal? a #=> false
h.key(200).equal? b #=> true
to_a → array Show source 
static VALUE
rb_hash_to_a(VALUE hash)
{
    VALUE ary;

    ary = rb_ary_new_capa(RHASH_SIZE(hash));
    rb_hash_foreach(hash, to_a_i, ary);

    return ary;
}

Converts hsh to a nested array of [ key, value ] arrays.

h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300  }
h.to_a   #=> [["c", 300], ["a", 100], ["d", 400]]
to_h → hsh or new_hash Show source
to_h {|key, value| block } → new_hash 
static VALUE
rb_hash_to_h(VALUE hash)
{
    if (rb_block_given_p()) {
        return rb_hash_to_h_block(hash);
    }
    if (rb_obj_class(hash) != rb_cHash) {
        const VALUE flags = RBASIC(hash)->flags;
        hash = hash_dup(hash, rb_cHash, flags & RHASH_PROC_DEFAULT);
    }
    return hash;
}

Returns self. If called on a subclass of Hash, converts the receiver to a Hash object.

If a block is given, the results of the block on each pair of the receiver will be used as pairs.

to_hash → hsh Show source 
static VALUE
rb_hash_to_hash(VALUE hash)
{
    return hash;
}

Returns self.

to_proc → proc Show source 
static VALUE
rb_hash_to_proc(VALUE hash)
{
    return rb_func_proc_new(hash_proc_call, hash);
}

Returns a Proc which maps keys to values.

h = {a:1, b:2}
hp = h.to_proc
hp.call(:a)          #=> 1
hp.call(:b)          #=> 2
hp.call(:c)          #=> nil
[:a, :b, :c].map(&h) #=> [1, 2, nil]
to_s()
Alias for: inspect
transform_keys {|key| block } → new_hash Show source
transform_keys → an_enumerator 
static VALUE
rb_hash_transform_keys(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_foreach(hash, transform_keys_i, result);
    }

    return result;
}

Returns a new hash with the results of running the block once for every key. This method does not change the values.

h = { a: 1, b: 2, c: 3 }
h.transform_keys {|k| k.to_s }  #=> { "a" => 1, "b" => 2, "c" => 3 }
h.transform_keys(&:to_s)        #=> { "a" => 1, "b" => 2, "c" => 3 }
h.transform_keys.with_index {|k, i| "#{k}.#{i}" }
                                #=> { "a.0" => 1, "b.1" => 2, "c.2" => 3 }

If no block is given, an enumerator is returned instead.

transform_keys! {|key| block } → hsh Show source
transform_keys! → an_enumerator 
static VALUE
rb_hash_transform_keys_bang(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        long i;
        VALUE pairs = rb_hash_flatten(0, NULL, hash);
        rb_hash_clear(hash);
        for (i = 0; i < RARRAY_LEN(pairs); i += 2) {
            VALUE key = RARRAY_AREF(pairs, i), new_key = rb_yield(key),
                  val = RARRAY_AREF(pairs, i+1);
            rb_hash_aset(hash, new_key, val);
        }
    }
    return hash;
}

Invokes the given block once for each key in hsh, replacing it with the new key returned by the block, and then returns hsh. This method does not change the values.

h = { a: 1, b: 2, c: 3 }
h.transform_keys! {|k| k.to_s }  #=> { "a" => 1, "b" => 2, "c" => 3 }
h.transform_keys!(&:to_sym)      #=> { a: 1, b: 2, c: 3 }
h.transform_keys!.with_index {|k, i| "#{k}.#{i}" }
                                 #=> { "a.0" => 1, "b.1" => 2, "c.2" => 3 }

If no block is given, an enumerator is returned instead.

transform_values {|value| block } → new_hash Show source
transform_values → an_enumerator 
static VALUE
rb_hash_transform_values(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = hash_copy(hash_alloc(rb_cHash), hash);
    SET_DEFAULT(result, Qnil);

    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_stlike_foreach_with_replace(result, transform_values_foreach_func, transform_values_foreach_replace, result);
    }

    return result;
}

Returns a new hash with the results of running the block once for every value. This method does not change the keys.

h = { a: 1, b: 2, c: 3 }
h.transform_values {|v| v * v + 1 }  #=> { a: 2, b: 5, c: 10 }
h.transform_values(&:to_s)           #=> { a: "1", b: "2", c: "3" }
h.transform_values.with_index {|v, i| "#{v}.#{i}" }
                                     #=> { a: "1.0", b: "2.1", c: "3.2" }

If no block is given, an enumerator is returned instead.

transform_values! {|value| block } → hsh Show source
transform_values! → an_enumerator 
static VALUE
rb_hash_transform_values_bang(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);

    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_stlike_foreach_with_replace(hash, transform_values_foreach_func, transform_values_foreach_replace, hash);
    }

    return hash;
}

Invokes the given block once for each value in hsh, replacing it with the new value returned by the block, and then returns hsh. This method does not change the keys.

h = { a: 1, b: 2, c: 3 }
h.transform_values! {|v| v * v + 1 }  #=> { a: 2, b: 5, c: 10 }
h.transform_values!(&:to_s)           #=> { a: "2", b: "5", c: "10" }
h.transform_values!.with_index {|v, i| "#{v}.#{i}" }
                                      #=> { a: "2.0", b: "5.1", c: "10.2" }

If no block is given, an enumerator is returned instead.

update(other_hash1, other_hash2, ...) → hsh Show source
update(other_hash1, other_hash2, ...) {|key, oldval, newval| block} 
static VALUE
rb_hash_update(int argc, VALUE *argv, VALUE self)
{
    int i;
    bool block_given = rb_block_given_p();

    rb_hash_modify(self);
    for (i = 0; i < argc; i++){
       VALUE hash = to_hash(argv[i]);
       if (block_given) {
           rb_hash_foreach(hash, rb_hash_update_block_i, self);
       }
       else {
           rb_hash_foreach(hash, rb_hash_update_i, self);
       }
    }
    return self;
}

Adds the contents of the given hashes to the receiver.

If no block is given, entries with duplicate keys are overwritten with the values from each other_hash successively, otherwise the value for each duplicate key is determined by calling the block with the key, its value in the receiver and its value in each other_hash.

h1 = { "a" => 100, "b" => 200 }
h1.merge!          #=> {"a"=>100, "b"=>200}
h1                 #=> {"a"=>100, "b"=>200}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h1.merge!(h2)      #=> {"a"=>100, "b"=>246, "c"=>300}
h1                 #=> {"a"=>100, "b"=>246, "c"=>300}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3)
                   #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}
h1                 #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3) {|key, v1, v2| v1 }
                   #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}
h1                 #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}

Hash#update is an alias for Hash#merge!.

value?(value) → true or false Show source 
static VALUE
rb_hash_has_value(VALUE hash, VALUE val)
{
    VALUE data[2];

    data[0] = Qfalse;
    data[1] = val;
    rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
    return data[0];
}

Returns true if the given value is present for some key in hsh.

h = { "a" => 100, "b" => 200 }
h.value?(100)   #=> true
h.value?(999)   #=> false
values → array Show source 
VALUE
rb_hash_values(VALUE hash)
{
    VALUE values;
    st_index_t size = RHASH_SIZE(hash);

    values = rb_ary_new_capa(size);
    if (size == 0) return values;

    if (ST_DATA_COMPATIBLE_P(VALUE)) {
        if (RHASH_AR_TABLE_P(hash)) {
            rb_gc_writebarrier_remember(values);
            RARRAY_PTR_USE_TRANSIENT(values, ptr, {
                size = ar_values(hash, ptr, size);
            });
        }
        else if (RHASH_ST_TABLE_P(hash)) {
            st_table *table = RHASH_ST_TABLE(hash);
            rb_gc_writebarrier_remember(values);
            RARRAY_PTR_USE_TRANSIENT(values, ptr, {
                size = st_values(table, ptr, size);
            });
        }
        rb_ary_set_len(values, size);
    }
    else {
        rb_hash_foreach(hash, values_i, values);
    }

    return values;
}

Returns a new array populated with the values from hsh. See also Hash#keys.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.values   #=> [100, 200, 300]
values_at(key, ...) → array Show source 
VALUE
rb_hash_values_at(int argc, VALUE *argv, VALUE hash)
{
    VALUE result = rb_ary_new2(argc);
    long i;

    for (i=0; i<argc; i++) {
        rb_ary_push(result, rb_hash_aref(hash, argv[i]));
    }
    return result;
}

Return an array containing the values associated with the given keys. Also see Hash.select.

h = { "cat" => "feline", "dog" => "canine", "cow" => "bovine" }
h.values_at("cow", "cat")  #=> ["bovine", "feline"]

Ruby Core © 1993–2017 Yukihiro Matsumoto
Licensed under the Ruby License.
Ruby Standard Library © contributors
Licensed under their own licenses.