Gabor Grothendieck wrote:
On Fri, Jan 9, 2009 at 4:28 PM, Wacek Kusnierczyk <Waclaw.Marcin.Kusnierczyk at idi.ntnu.no> wrote:
Rau, Roland wrote:
P.S. Any suggestions how to become more proficient with regular
expressions? The O'Reilly book ("Mastering...")? Whenever I tried
anything more complicated than basic usage (things like ^ $ * . ) in R,
I was way faster to write a new function (like above) instead of finding
a regex solution.
the book you mention is good. you may also consider http://www.regular-expressions.info/ regexes are usually well explained with lots of examples in perl books.
By the way: it might be still possible to *write* regular expressions,
but what about code re-use? Are there people who can easily *read*
complicated regular expressions?
in some cases it is possible to write regular expressions in a way that
facilitates reading them by a human. in perl, for example, you can use
so-called readable regexes:
/
(.+) # match and remember at least one arbitrary character
[.] # match a dot
[^.]+ # match at least one non-dot character
$ # end of string anchor
/x;
you can also use within regex comments:
/(.+)(?# one or more chars)[.](?# a dot)[^.]+(?# one or more
non-dots)$(?# end of string)/
nothing of the sorts in r, however.
Supports that if you begin the regular expression with (?x) and use perl = TRUE. See ?regexp
cool, i see ?xism is supported. so the above can be written in r as:
names = c("foo.bar", ".zee")
sub("(?x) # alloow embedded comemnts
(.+) # match and remember at least one arbitrary character
[.] # match a dot
[^.]+ # match at least one non-dot character
$ # end of string anchor",
"\\1", names, perl=TRUE)
is this what you wanted, roland?
vQ