Duncan Murdoch ha scritto:
On 11/16/2009 8:21 AM, Ottorino-Luca Pantani wrote:
Dear R users,
my problem today deals with my ignorance on regular expressions.
a matter I recently discovered.
You were close. First, gsub by default doesn't need escapes before
the parens. (There are lots of different conventions for regular
expressions, unfortunately.) So the Emacs regular expression V_\(.\)_
is entered as "V_(.)_" in the default version of gsub(). Second, to
enter a backslash into a string, you need to escape it. So the
replacement pattern V_0\1_ is entered as "V_0\\1_". So
gsub("V_(.)_", "V_0\\1_", foo)
should give you what you want.
Duncan Murdoch
Any of these (the need for doubling of the "\\" for the
back-reference seems to be the main issue:
> gsub("_([[:digit:]])_.", "_0\\1_", foo)
> gsub("_(\\d)_.", "_0\\1_", foo)
> gsub("V_(.)_", "V_0\\1_", foo)
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
I suspected something on the double escape..........
Thanks to you all.
R is a wonderful software and R-help is always a great place to visit !!!
8rino
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