I am using stopifnot
and I understand it just returns the first value that was not TRUE
. I f that is some freaky dynamic expression someone who is not into the custom function cannot really make something out of that. So I would love to add a custom error message. Any suggestions?
Error: length(unique(nchar(check))) == 1 is not TRUE
Basically states that the elements of the vector check
do not have the same length.
Is there a way of saying: Error: Elements of your input vector do not have the same length!
?
Use stop
and an if
statement:
if(length(unique(nchar(check))) != 1)
stop("Error: Elements of your input vector do not have the same length!")
Just remember that stopifnot
has the convenience of stating the negative, so your condition in the if
needs to be the negation of your stop condition.
This is what the error message looks like:
> check = c("x", "xx", "xxx")
> if(length(unique(nchar(check))) != 1)
+ stop("Error: Elements of your input vector do not have the same length!")
Error in eval(expr, envir, enclos) :
Error: Elements of your input vector do not have the same length!
A custom message can be added as a label to your expression:
stopifnot("Elements of your input vector do not have the same length!" =
length(unique(nchar(check))) == 1)
# Error: Elements of your input vector do not have the same length!
The assertive
and assertthat
packages have more readable check functions.
library(assertthat)
assert_that(length(unique(nchar(check))) == 1)
## Error: length(unique(nchar(check))) == 1 are not all true.
library(assertive)
assert_is_scalar(unique(nchar(check)))
## Error: unique(nchar(check)) does not have length one.
if(!is_scalar(unique(nchar(check))))
{
stop("Elements of check have different numbers of characters.")
}
## Error: Elements of check have different numbers of characters.
Or you could package it up.
assert <- function (expr, error) {
if (! expr) stop(error, call. = FALSE)
}
So you have:
> check = c("x", "xx", "xxx")
> assert(length(unique(nchar(check))) == 1, "Elements of your input vector do not have the same length!")
Error: Elements of your input vector do not have the same length!
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