Re: [Rd] sub('^', .....) bugs (PR#7742)

From: Gabor Grothendieck <ggrothendieck_at_myway.com>
Date: Wed 23 Mar 2005 - 09:45:16 GMT

 <maechler <at> stat.math.ethz.ch> writes:

:
: >>>>> "David" == David Forrest <drf5n <at> maplepark.com>
: >>>>> on Tue, 22 Mar 2005 15:02:20 -0600 (CST) writes:
:
: David> According to help(sub), the ^ should match the
: David> zero-length string at the beginning of a string:
:
: yes, indeed.
:
: David> sub('^','var',1:3) # "1" "2" "3"
: David> sub('$','var',1:3) # "1var" "2var" "3var"
:
: David> # This generates what I expected from the first case:
: David> sub('^.','var',11:13) # "var1" "var2" "var3"
:
: there are even more fishy things here:
:
: 1) In your cases, the integer 'x' argument is auto-coerced to
: character, however that fails as soon as 'perl = TRUE' is used.
:
: > sub('^','v_', 1:3, perl=TRUE)
: Error in sub.perl(pattern, replacement, x, ignore.case) :
: invalid argument
:
: {one can argue that this is not a bug, since the help file asks
: for 'x' to be a character vector; OTOH, we have
: as.character(.) magic in many other places, i.e. quite
: naturally here;
: at least perl=TRUE and perl=FALSE should behave consistently.}
:
: 2) The 'perl=TRUE' case behaves even more problematically here:
:
: > sub('^','v_', LETTERS[1:3], perl=TRUE)
: [1] "A\0e" "B\0J" "C\0S"
: > sub('^','v_', LETTERS[1:3], perl=TRUE)
: [1] "A\0J" "B\0P" "C\0J"
: > sub('^','v_', LETTERS[1:3], perl=TRUE)
: [1] "A\0\0" "B\0\0" "C\0m"
: >
:
: i.e., the result is random nonsense.
:
: Note that this happens both for R-patched (2.0.1) and R-devel (2.1.0 alpha).
:
: ==> "forwarded" as bug report to R-bugs

Also consider the following which may be related. #1 does not place an X before the first word and #2 causes R to hang.

R> R.version.string # Windows XP
[1] "R version 2.1.0, 2005-03-17"

R> gsub("\\b", "X", "The quick brown fox") # 1 [1] "The Xquick Xbrown Xfox"

R> gsub("\\b", "X", "The quick brown fox", perl = TRUE) # 2 ... hangs ...



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https://stat.ethz.ch/mailman/listinfo/r-devel Received on Wed Mar 23 20:50:46 2005

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