stopifnot() suggestion

Wouldn't it be better to do something like

stopifnot(all(!is.na(x)), all(!is.na(y)), x, y)

rather than have stopifnot() go checking for NAs?  I agree the message is 
strange but if having non-NA values is really a condition, then why not just 
put it in the call to stopifnot()?

-roger

I was thinking of a fallible R user accidentally testing the truth of an 
expression with NAs, rather than of a situation where you remember that 
there may be missing values. For example
f <- function() { x <- NA ; if(x != 4) stop("x should be 4") }
g <- function() { x <- NA ; stopifnot(x == 4) }
f()
Error in if (x != 4) stop("x should be 4") :
 	missing value where TRUE/FALSE needed
g()
Error in if (!(is.logical(r <- eval(ll[[i]])) && all(r))) 
stop(paste(deparse(mc[[i +  :
 	missing value where TRUE/FALSE needed

If you write the error-checking code represented by f(), you get a message 
which is very helpful in correcting your error. But someone who uses 
stopifnot() instead gets the output of g(). Even a user who knows the 
origin of the code in the error message doesn't know which of several 
stopifnot()s is responsible.

Dan
Dan Davison wrote:
If an expression is passed to stopifnot() which contains missing values, 
then the resulting error message is somewhat baffling until you are used to 
it, e.g.

x <- y <- rep(TRUE, 10)
y[7] <- NA
stopifnot(x, y)
Error in if (!(is.logical(r <- eval(ll[[i]])) && all(r))) 
stop(paste(deparse(mc[[i +  :
 	missing value where TRUE/FALSE needed

A minor change to stopifnot() produces the following behaviour:

stopifnot(x, y)
Error in stopifnot(x, y) : y contains missing values

My attempt at a suitable modification follows, and below that the original 
function definition. Is a change along these lines appropriate?

## Altered version

stopifnot <- function (...) {
     n <- length(ll <- list(...))
     if (n == 0)
         return(invisible())
     mc <- match.call()
     for (i in 1:n) {
         if(any(is.na(r <- eval(ll[[i]])))) stop(paste(deparse(mc[[i + 
1]])), " contains missing values")
         if (!(is.logical(r) && all(r)))
             stop(paste(deparse(mc[[i + 1]]), "is not TRUE"), call. = 
FALSE)
     }
}

## from R-2.1.1/src/library/base/R/stop.R

stopifnot <- function(...)
{
     n <- length(ll <- list(...))
     if(n == 0)
         return(invisible())
     mc <- match.call()
     for(i in 1:n)
         if(!(is.logical(r <- eval(ll[[i]])) && all(r)))
             stop(paste(deparse(mc[[i+1]]), "is not TRUE"), call. = FALSE)
}

Thanks,

Dan

version
          _
platform i386-pc-linux-gnu
arch     i386
os       linux-gnu
system   i386, linux-gnu
status
major    2
minor    2.0
year     2005
month    10
day      06
svn rev  35749
language R

----------
Dan Davison
Committee on Evolutionary Biology
University of Chicago, U.S.A.

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-- 
Roger D. Peng  |  http://www.biostat.jhsph.edu/~rpeng/

stopifnot() suggestion

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