stopifnot

From base v3.6.2 by R-core R-core@R-project.org

Ensure the Truth of R Expressions

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.

Keywords: programming, environment, error

Usage

stopifnot(…, exprs, local = TRUE)

Arguments

…, exprs

any number of (typically but not necessarily logical) R expressions, which should each evaluate to (a logical vector of all) TRUE. Use either … or exprs, the latter typically an unevaluated expression of the form

{
   expr1
   expr2
   ....
}

local

(only when exprs is used:) indicates the environment in which the expressions should be evaluated; by default the one where stopifnot() has been called from.

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. Further, when such an expression signals an error or warning, the message produced no longer contains the full stopifnot call, but just the erroneous expression.

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.

Examples

library(base)

# NOT RUN {
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(all.equal(pi, 3.141593),  2 < 2, all(1:10 < 12), "a" < "b")
## More convenient for interactive "line by line" evaluation:
stopifnot(exprs = {
  all.equal(pi, 3.1415927)
  2 < 2
  all(1:10 < 12)
  "a" < "b"
})

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

options(op)  # revert to previous error handler
# }

Documentation reproduced from package base, version 3.6.2, License: Part of R 3.6.2

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