On Wed, 23 Mar 2005, Brian D Ripley wrote:
The first is as designed: zero-length initial matches are ignored in the C code. (Don't ask me why it was designed that way.)
The second is not reproducible in the current sources, so is probably already fixed by the fix to PR#7742.
I've found a better solution for the perl=T internal code:
gsub("\\b", "X", "The quick brown fox", perl = TRUE)
[1] "XTheX XquickX XbrownX XfoxX"
but not yet for the standard case, because of the design limitations.
On Wed, 23 Mar 2005, Gabor Grothendieck wrote:
<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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-- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595
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-- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595
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