class CSV
Overview
Provides methods and classes for parsing and generating CSV (comma-separated values) strings.
This module conforms to RFC 4180.
Parsing
Several ways of parsing CSV are provided. The most straight-forward, but slow or inefficient for some scenarios, is CSV#parse
, which returns an array of arrays of all data.
Rows can be traversed in a linear fashion with CSV#each_row
, or using an Iterator
.
To parse a CSV in an efficient way, optionally being able to access row values from header names, create an instance of a CSV
.
Parsing with CSV#new
A CSV instance holds a cursor to the current row in the CSV. The cursor is advanced by invoking #next
, which returns true
if a next row was found, and false
otherwise. A first call to #next
is required to position the CSV parser in the first row.
Once positioned in a row, values can be obtained with the several #[]
methods, which can accept a header name, column position, or header name pattern as a Regex
.
Additionally, a Row
object can be obtained with the #row
method which provides similar methods and can be converted to an Array
or Hash
.
Example
require "csv" csv = CSV.new("Name, Age\nJohn, 20\nPeter, 30", headers: true) csv.next # => true csv["Name"] # => "John" csv[0] # => "John" csv[-2] # => "John" csv[/name/i] # => "John" csv["Age"] # => " 20" csv.row.to_a # => ["John", " 20"] csv.row.to_h # => {"Name" => "John", "Age" => " 20"} csv.next # => true csv["Name"] # => "Peter" csv.next # => false
Building
To create CSV data, check CSV#build
and the CSV::Builder
class.
Defined in:
csv.crcsv/error.cr
Constant Summary
- DEFAULT_QUOTE_CHAR =
'"'
- DEFAULT_SEPARATOR =
','
Constructors
- .new(string_or_io : String | IO, headers = false, strip = false, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR)
- .new(string_or_io : String | IO, headers = false, strip = false, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, &)
Class Method Summary
- .build(separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, quoting : Builder::Quoting = Builder::Quoting::RFC, &) : String
Builds a CSV.
- .build(io : IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, quoting : Builder::Quoting = Builder::Quoting::RFC, &) : Nil
Appends CSV data to the given
IO
. - .each_row(string_or_io : String | IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, &)
- .each_row(string_or_io : String | IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR)
- .parse(string_or_io : String | IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR) : Array(Array(String))
Parses a CSV or
IO
into an array.
Instance Method Summary
- #[](header : String) : String
Returns the current row's value corresponding to the given header name.
- #[](column : Int) : String
Returns the current row's value at the given column index.
- #[](header_pattern : Regex) : String
Returns the current row's value corresponding to the given header_pattern.
- #[]?(header : String) : String?
Returns the current row's value corresponding to the given header name.
- #[]?(column : Int) : String?
Returns the current row's value at the given column index.
- #[]?(header_pattern : Regex) : String?
Returns the current row's value corresponding to the given header_pattern.
- #each(&) : Nil
Invokes the block once for each row in this CSV, yielding
self
. - #headers : Array(String)
Returns this CSV headers.
- #next : Bool
Advanced the cursor to the next row.
- #rewind : Nil
Rewinds this CSV to the beginning, rewinding the underlying IO if any.
- #row : Row
Returns the current row as a
Row
instance. - #values_at(*columns : Int)
Returns a tuple of the current row's values at given indices A negative index counts from the end.
- #values_at(*headers : String)
Returns a tuple of the current row's values corresponding to the given headers Raises
KeyError
if any header doesn't exist.
Instance methods inherited from class Reference
==(other : self)==(other : JSON::Any)
==(other : YAML::Any)
==(other) ==, dup dup, hash(hasher) hash, inspect(io : IO) : Nil inspect, object_id : UInt64 object_id, pretty_print(pp) : Nil pretty_print, same?(other : Reference) : Bool
same?(other : Nil) same?, to_s(io : IO) : Nil to_s
Constructor methods inherited from class Reference
new new Instance methods inherited from class Object
! : Bool !, !=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)===(other : YAML::Any)
===(other) ===, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash(hasher)
hash hash, in?(collection : Object) : Bool
in?(*values : Object) : Bool in?, inspect(io : IO) : Nil
inspect : String inspect, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) tap, to_json(io : IO) : Nil
to_json : String to_json, to_pretty_json(indent : String = " ") : String
to_pretty_json(io : IO, indent : String = " ") : Nil to_pretty_json, to_s(io : IO) : Nil
to_s : String to_s, to_yaml(io : IO) : Nil
to_yaml : String to_yaml, try(&) try, unsafe_as(type : T.class) forall T unsafe_as
Class methods inherited from class Object
from_json(string_or_io, root : String)from_json(string_or_io) from_json, from_yaml(string_or_io : String | IO) from_yaml
Constructor Detail
def self.new(string_or_io : String | IO, headers = false, strip = false, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR)Source
Creates a new instance from the given String
or IO
.
- If strip is
true
, row values are stripped withString#strip
before being returned from methods. - If headers is
true
, row values can be accessed with header names or patterns. Headers are always stripped.
See CSV.parse
about the separator and quote_char arguments.
def self.new(string_or_io : String | IO, headers = false, strip = false, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, &)Source
Creates a new instance from the given String
or IO
, and yields it to the given block once for each row in the CSV.
- If strip is
true
, row values are stripped withString#strip
before being returned from methods. - If headers is
true
, row values can be accessed with header names or patterns. Headers are always stripped.
See CSV.parse
about the separator and quote_char arguments.
Class Method Detail
def self.build(separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, quoting : Builder::Quoting = Builder::Quoting::RFC, &) : StringSource
Builds a CSV. This yields a CSV::Builder
to the given block.
Takes optional quoting argument to define quote behavior.
require "csv" result = CSV.build do |csv| csv.row "one", "two" csv.row "three" end result # => "one,two\nthree\n" result = CSV.build(quoting: CSV::Builder::Quoting::ALL) do |csv| csv.row "one", "two" csv.row "three" end result # => "\"one\",\"two\"\n\"three\"\n"
def self.build(io : IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, quoting : Builder::Quoting = Builder::Quoting::RFC, &) : NilSource
Appends CSV data to the given IO
. This yields a CSV::Builder
that writes to the given IO
.
require "csv" io = IO::Memory.new io.puts "HEADER" CSV.build(io) do |csv| csv.row "one", "two" csv.row "three" end io.to_s # => "HEADER\none,two\nthree\n"
def self.each_row(string_or_io : String | IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, &)Source
def self.each_row(string_or_io : String | IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR)Source
def self.parse(string_or_io : String | IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR) : Array(Array(String))Source
Parses a CSV or IO
into an array.
Takes optional separator and quote_char arguments for defining non-standard csv cell separators and quote characters.
require "csv" CSV.parse("one,two\nthree") # => [["one", "two"], ["three"]] CSV.parse("one;two\n'three;'", separator: ';', quote_char: '\'') # => [["one", "two"], ["three;"]]
Instance Method Detail
def [](header : String) : StringSource
Returns the current row's value corresponding to the given header name. Raises KeyError
if no such header exists. Raises CSV::Error
if headers were not requested.
def [](column : Int) : StringSource
Returns the current row's value at the given column index. A negative index counts from the end. Raises IndexError
if no such column exists.
def [](header_pattern : Regex) : StringSource
Returns the current row's value corresponding to the given header_pattern. Raises KeyError
if no such header exists. Raises CSV::Error
if headers were not requested.
def []?(header : String) : String?Source
Returns the current row's value corresponding to the given header name. Returns nil
if no such header exists. Raises CSV::Error
if headers were not requested.
def []?(column : Int) : String?Source
Returns the current row's value at the given column index. A negative index counts from the end. Returns nil
if no such column exists.
def []?(header_pattern : Regex) : String?Source
Returns the current row's value corresponding to the given header_pattern. Returns nil
if no such header exists. Raises CSV::Error
if headers were not requested.
def headers : Array(String)Source
Returns this CSV headers. Their values are always stripped. Raises CSV::Error
if headers were not requested.
def next : BoolSource
Advanced the cursor to the next row. Must be called once to position the cursor in the first row. Returns true
if a next row was found, false
otherwise.
def values_at(*columns : Int)Source
Returns a tuple of the current row's values at given indices A negative index counts from the end. Raises IndexError
if any column doesn't exist The behavior of returning a tuple is similar to Hash#values_at
def values_at(*headers : String)Source
Returns a tuple of the current row's values corresponding to the given headers Raises KeyError
if any header doesn't exist. Raises CSV::Error
if headers were not requested The behavior of returning a tuple is similar to Hash#values_at
© 2012–2021 Manas Technology Solutions.
Licensed under the Apache License, Version 2.0.
https://crystal-lang.org/api/1.2.1/CSV.html