[Rd] Use of all/any
maechler at stat.math.ethz.ch
Fri Oct 26 18:18:08 CEST 2007
>>>>> "BDR" == Prof Brian Ripley <ripley at stats.ox.ac.uk>
>>>>> on Fri, 26 Oct 2007 08:16:03 +0100 (BST) writes:
BDR> all/any coerce their arguments to logical (if
BDR> possible). I've added a warning in R-devel if coercion
BDR> is from something other than integer.
BDR> This arose because it is easy to make a slip and write
BDR> all(X) > 0 rather than all(X > 0): thanks to Bill
BDR> Dunlap for bringing that to my attention.
BDR> However, it has been useful in detecting quite a few other things:
BDR> - indices which had been made double where integer was
BDR> intended. One example from predict.lm was
BDR> iipiv[ii == 0] <- 0
BDR> which was intended to be
BDR> iipiv[ii == 0L] <- 0L
Hmm.... Do we really want to generate warnings for such small
I'm very happy that we've introduced <n>L integer notation, and
as a subtle programmer, I'm making use of it gladly --- but
still not always, just for code beauty reasons ("0" reads better).
On the other hand, I don't think the casual R / S programmer
should get warnings; after all, S and R are not C on purpose.
Apropos Bill Dunlap's note: Do newer versions of S-plus warn?
At least up to 6.2.2, I'm pretty sure no S version has warned
X <- c(0.1, pi)
all(X) > 0.5
In spite, of the buglets of you have revealed, mentioned below,
currently, I'd still tend to only warn for coercion from
non-numeric, but not from double.
In this context, I have thought again of using *levels* of
warnings, configurable via options(), and we could activate more
stringent warnings when "R CMD check"ing than per default.
Actually, we already have a simple form of that (with I think message()),
and also with the way the 'codetools' ``warnings'' are treated
by 'R CMD check'.
For my taste and "S language feeling", such a
'double -> logical coercion warning'
is somewhat similar in sprit to some of the codetools warnings.
BDR> - uses of lapply where sapply was intended. Examples
BDR> are of the form
BDR> all(lapply(z, is.numeric))
BDR> which is applying all() to a list. One might worry
BDR> sapply(z, is.numeric)
BDR> will return a list if length(z) == 0 (which it does)
BDR> and so all() would warn, but that is covered by another
BDR> change, to ignore all length-zero arguments (and so
BDR> avoid the cost of coercion to logical(0)).
BDR> I decided not to warn on integer as it is so common.
BDR> But at least some of these are thinkos. For example,
BDR> constructions like
BDR> all(grep(pattern, x))
BDR> occurred scores of times in the R sources. Since the
BDR> value of grep() is an integer vector of positive
BDR> indices, this is equivalent to
BDR> length(grep(pattern, x)) > 0
BDR> and when used in a if() condition the '> 0' is not
BDR> Some warnings are common from other packages: one is
BDR> Warning in any(textLocations) : coercing argument of
BDR> type 'double' to logical
BDR> from lattice (and Deepayan Sarkar will fix that
BDR> shortly). Quite a few others looked familiar but are
BDR> the result of package authors copying code from base R
BDR> or other packages: if you do that you do need to copy
BDR> the bugfixes too.
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