Martin Maechler <maech...@stat.math.ethz.ch> wrote:
> I don't mind putting together a minimal package with some prototypes, tests,
> comparisons, etc. But perhaps we should aim for consensus on a few issues
> beforehand. (Sorry if these have been discussed to death already elsewhere.
> In that case, links to relevant threads would be helpful ...)
>
> 1. Should the type and class attribute of the return value be exactly the
> type and class attribute of c(yes[0L], no[0L]), independent of 'test'?
> Or something else?
>
> 2. What should be the attributes of the return value (other than
> 'class')?
>
> base::ifelse keeps attributes(test) if 'test' is atomic, which seems
> like desirable behaviour, though dplyr and data.table seem to think
> otherwise:
In my experience, base::ifelse keeping attributes of 'test' is useful for names.
It may also be useful for dimensions, but for other attributes, it may be a
dangerous feature.
Otherwise, attributes of c(yes, no) should be mostly preserved in my opinion.
> 3. Should the new function be stricter and/or more verbose? E.g., should
> it signal a condition if length(yes) or length(no) is not equal to 1
> nor length(test)?
To be consistent with base R, it should warn if length(yes), length(no) and
length(test) are not divisors of the longest, otherwise silently repeat the
three vectors to get the same sizes.
This would work consistently with mathematical operators such as test+yes+no.
In my personal experience, the truncation of 'yes' and 'no' to length(test) if
the most dangerous feature of ifelse().
> 4. Should the most common case, in which neither 'yes' nor 'no' has a
> 'class' attribute, be handled in C? The remaining cases might rely on
> method dispatch and thus require a separate "generic" implementation in
> R. How much faster/more efficient would the C implementation have to
> be to justify the cost (more maintenance for R-core, more obfuscation
> for the average user)?
If the function is not much slower than today ifelse(), it is not worth
rewriting in C in my opinion.
Thank you for an implementation!
A few examples of misbehaviors (in my opinion):
> ifelse2(c(a=TRUE), factor("a"), factor("b"))
Error in as.character.factor(x) : malformed factor
> ifelse2(TRUE, factor(c("a","b")), factor(c("b","a")))
[1] a
Levels: a b
I would expect this one to output
[1] a b
Levels: a b
I tried to develop a function that behaves like mathematical operators (e.g.
test+yes+no) for length & dimensions coercion rules.
Please, find the function and a few tests below:
ifelse2 <- function (test, yes, no) {
# forces evaluation of arguments in order
test
yes
no
if (is.atomic(test)) {
if (!is.logical(test))
storage.mode(test) <- "logical"
}
else test <- if (isS4(test)) methods::as(test, "logical") else
as.logical(test)
ntest <- length(test)
nyes <- length(yes)
nno <- length(no)
nn <- c(ntest, nyes, nno)
nans <- max(nn)
ans <- rep(c(yes[0L], no[0L]), length.out=nans)
# check dimension consistency for arrays
has.dim <- FALSE
if (length(dim(test)) | length(dim(yes)) | length(dim(no))) {
lparams <- list(test, yes, no)
ldims <- lapply(lparams, dim)
ldims <- ldims[!sapply(ldims, is.null)]
ldimnames <- lapply(lparams, dimnames)
ldimnames <- ldimnames[!sapply(ldimnames, is.null)]
rdim <- ldims[[1]]
rdimnames <- ldimnames[[1]]
for(d in ldims) {
if (!identical(d, rdim)) {
stop(gettext("non-conformable arrays"))
}
}
has.dim <- TRUE
}
if (any(nans %% nn)) {
warning(gettext("longer object length is not a multiple of
shorter object length"))
}
if (ntest != nans) {test <- rep(test, length.out=nans)}
if (nyes != nans) {yes <- rep(yes, length.out=nans)}
if (nno != nans) {no <- rep(no, length.out=nans)}
idx <- which( test)
ans[idx] <- yes[idx]
idx <- which(!test)
ans[idx] <- no[idx]
if (has.dim) {
dim(ans) <- rdim
dimnames(ans) <- rdimnames
}
if (!is.null(names(test))) {
names(ans) <- names(test)
}
ans
}
ifelse2(c(alpha=TRUE,beta=TRUE,gamma=FALSE),factor(c("A","B","C","X")),factor(c("A","B","C","D")))
ifelse2(c(TRUE,FALSE), as.Date("2025-04-01"), c("2020-07-05", "2022-07-05"))
ifelse2(c(a=TRUE, b=FALSE,c=TRUE,d=TRUE), list(42), list(40,45))
ifelse2(rbind(alpha=c(a=TRUE, b=FALSE),beta=c(c=TRUE,d=FALSE)), list(1:10),
list(2:20,3:30))
a=rbind(alpha=c(a=TRUE, b=FALSE),beta=c(TRUE,TRUE))
b=rbind(ALPHA=c(A=TRUE, B=FALSE),BETA=c(C=TRUE,D=TRUE))
c=rbind(ALPHA2=c(A2=TRUE, B2=FALSE),BETA2=c(C2=TRUE,D2=TRUE))
ifelse2(a,b,c)
dimnames(a) <- NULL
ifelse2(a,b,c)
dimnames(b) <- NULL
ifelse2(a,b,c)
--
Sincerely
André GILLIBERT
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