stopifnot Ensure the Truth of R Expressions

Description

If any of the expressions (in ... or exprs) are not all TRUE, stop is called, producing an error message indicating the first expression which was not (all) true.

Usage

stopifnot(..., exprs, exprObject, local = TRUE)

Arguments

{
   expr1
   expr2
   ....
}

Details

This function is intended for use in regression tests or also argument checking of functions, in particular to make them easier to read.

stopifnot(A, B) or equivalently stopifnot(exprs= {A ; B}) are conceptually equivalent to

 { if(any(is.na(A)) || !all(A)) stop(...);
   if(any(is.na(B)) || !all(B)) stop(...) }

Since R version 3.6.0, stopifnot() no longer handles potential errors or warnings (by tryCatch() etc) for each single expression and may use sys.call(<n>) to get a meaningful and short error message in case an expression did not evaluate to all TRUE. This provides considerably less overhead.

Since R version 3.5.0, expressions are evaluated sequentially, and hence evaluation stops as soon as there is a “non-TRUE”, as indicated by the above conceptual equivalence statement.

Also, since R version 3.5.0, stopifnot(exprs = { ... }) can be used alternatively and may be preferable in the case of several expressions, as they are more conveniently evaluated interactively (“no extraneous , ”).

Since R version 3.4.0, when an expression (from ...) is not true and is a call to all.equal, the error message will report the (first part of the) differences reported by all.equal(*).

Value

(NULL if all statements in ... are TRUE.)

Note

Trying to use the stopifnot(exprs = ..) version via a shortcut, say,

 assertWRONG <- function(exprs) stopifnot(exprs = exprs) 

is delicate and the above is not a good idea. Contrary to stopifnot() which takes care to evaluate the parts of exprs one by one and stop at the first non-TRUE, the above short cut would typically evaluate all parts of exprs and pass the result, i.e., typically of the last entry of exprs to stopifnot().

However, a more careful version,

 assert <- function(exprs) eval.parent(substitute(stopifnot(exprs = exprs))) 

may be a nice short cut for stopifnot(exprs = *) calls using the more commonly known verb as function name.

See Also

stop, warning; assertCondition in package tools complements stopifnot() for testing warnings and errors.

Examples

stopifnot(1 == 1, all.equal(pi, 3.14159265), 1 < 2) # all TRUE

m <- matrix(c(1,3,3,1), 2, 2)
stopifnot(m == t(m), diag(m) == rep(1, 2)) # all(.) |=>  TRUE

op <- options(error = expression(NULL))
# "disabling stop(.)"  << Use with CARE! >>

stopifnot(length(10)) # gives an error: '1' is *not* TRUE
## even when   if(1) "ok"   works

stopifnot(all.equal(pi, 3.141593),  2 < 2, (1:10 < 12), "a" < "b")
## More convenient for interactive "line by line" evaluation:
stopifnot(exprs = {
  all.equal(pi, 3.1415927)
  2 < 2
  1:10 < 12
  "a" < "b"
})

eObj <- expression(2 < 3, 3 <= 3:6, 1:10 < 2)
stopifnot(exprObject = eObj)
stopifnot(exprObject = quote(3 == 3))
stopifnot(exprObject = TRUE)


# long all.equal() error messages are abbreviated:
stopifnot(all.equal(rep(list(pi),4), list(3.1, 3.14, 3.141, 3.1415)))

# The default error message can be overridden to be more informative:
m[1,2] <- 12
stopifnot("m must be symmetric"= m == t(m))
#=> Error: m must be symmetric

options(op)  # revert to previous error handler