I would have thought that all 4 of the following
would give the same result (the first):
> gsub("backslash-X", "\\X", "this is a backslash-X", fixed=T)
[1] "this is a \\X"
> gsub("backslash-X", "\\X", "this is a backslash-X", extended=F)
[1] "this is a X"
> gsub("backslash-X", "\\X", "this is a backslash-X", extended=T)
[1] "this is a X"
> gsub("backslash-X", "\\X", "this is a backslash-X", perl=T)
[1] "this is a X"
If fixed==F the first "\\" is ignored except if it is followed by a
digit. In particular, the replacement string must use "\\\\" to insert
a backslash and "\\" by itself is the same as "". When fixed==T,
replacement="\\" means to insert a backslash.
I've seen code in package:gdata that depends on this behavior but I did
not see it described in help(gsub). It describes using
replacement="\\<digit>" to put a matched subpattern into the output,
but not the fact that replacement="\\<nondigit>" is equivalent to
replacement="<nondigit>" (but only when fixed==F).
Is that intended or is the help file incomplete? I'd like to
get Splus's gsub/substituteString in line with R's.
----------------------------------------------------------------------------
Bill Dunlap
Insightful Corporation
bill at insightful dot com
360-428-8146
"All statements in this message represent the opinions of the author and do
not necessarily reflect Insightful Corporation policy or position."
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