On 13-07-15 1:02 AM, Justin Talbot wrote:
The pmatch help (see also section 4.3.2 in the R Language Definition)
claims that pmatch with duplicates.ok=FALSE provides the same
functionality as R's argument matching algorithm, modulo how empty
strings are matched.
Here's an undocumented inconsistency between pmatch and R's argument
matching algorithm:
sessionInfo()
R version 3.0.1 (2013-05-16)
Platform: x86_64-apple-darwin10.8.0 (64-bit)
locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
attached base packages:
[1] stats graphics grDevices utils datasets methods base
f <- function(abc, ax) 1
f(ab=1,a=10)
Error in f(ab = 1, a = 10) :
formal argument "abc" matched by multiple actual arguments
pmatch(c('ab','a'), c('abc', 'ax'), duplicates.ok=FALSE)
[1] 1 2
That is, pmatch doesn't consider ambiguous partial matches to be an
error if the ambiguity is resolved by an earlier partial match.
This leads to an order dependency in pmatch that doesn't happen with
argument matching:
pmatch(c('ab','a'), c('abc', 'ax'), duplicates.ok=FALSE)
[1] 1 2
pmatch(c('a','ab'), c('abc', 'ax'), duplicates.ok=FALSE)
[1] NA 1
It would be great if this were documented.
Or should it be made consistent? Is there any value in keeping the
current pmatch behaviour different from the argument matching?
At a higher level, is pmatch intended to be the same as the argument
matching algorithm or is it just supposed to be "close"?
I would take that line in the documentation to say it is intended to be
the same except for empty strings.
Duncan Murdoch
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