R help - Nov 2004 - how to get to interesting part of pattern match

Hi,

I am looking for a way to extract an "interesting" part of the match
to
a regular expression. For example the pattern "[./](*.)" matches a
substring that begins with either "." or "/" followed by
anything. I am
interested in this "anything" w/o the "." or "/"
prefix. If say I match
the pattern against "abc/foo" I want to get "foo", not
"/foo". In Perl
one can simply wrap the "interesting" part in () and get it out of the
match. Is it possible to do a similar thing in R?

There seems to be a way to refer to the match, see below, but I couldn't
figure out how to make gsub return it.
> gsub("[./](*.)", "\\1", "abc/foo")
[1] "abcfoo"


Thanks,
Vadim

sub(".*/", "", "abc/foo")
[1] "foo"


Jean

On Thu, 18 Nov 2004, Vadim Ogranovich wrote:
> Hi,
>
> I am looking for a way to extract an "interesting" part of the
match to
> a regular expression. For example the pattern "[./](*.)" matches
a
> substring that begins with either "." or "/" followed
by anything. I am
> interested in this "anything" w/o the "." or
"/" prefix. If say I match
> the pattern against "abc/foo" I want to get "foo", not
"/foo". In Perl
> one can simply wrap the "interesting" part in () and get it out
of the
> match. Is it possible to do a similar thing in R?
>
> There seems to be a way to refer to the match, see below, but I
couldn't
> figure out how to make gsub return it.
> > gsub("[./](*.)", "\\1", "abc/foo")
> [1] "abcfoo"
>
>
> Thanks,
> Vadim
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>

Vadim Ogranovich <vograno <at> evafunds.com> writes:


: I am looking for a way to extract an "interesting" part of the match
to
: a regular expression. For example the pattern "[./](*.)" matches a
: substring that begins with either "." or "/" followed by
anything. I am
: interested in this "anything" w/o the "." or "/"
prefix. If say I match
: the pattern against "abc/foo" I want to get "foo", not
"/foo". In Perl
: one can simply wrap the "interesting" part in () and get it out of
the
: match. Is it possible to do a similar thing in R?
: 
: There seems to be a way to refer to the match, see below, but I couldn't
: figure out how to make gsub return it.
: > gsub("[./](*.)", "\\1", "abc/foo")
: [1] "abcfoo"

Assuming what was meant is the following (dot and star are 
transposed and gsub is sub):

	sub("[./](.*)", "\\1", "abc/foo")

then the regular expression matches /foo and the backreference
contains foo so it replaces /foo with foo which is why it returns
abcfoo .

To get just foo ensure that your regular expression matches 
the entire string so that the entire string is replaced with
the backreference:

	sub("[^./]*[./](.*)", "\\1", "abc/foo")

Vadim Ogranovich wrote:
>Hi,
>
>I am looking for a way to extract an "interesting" part of the
match to
>a regular expression. For example the pattern "[./](*.)" matches a
>substring that begins with either "." or "/" followed by
anything. I am
>interested in this "anything" w/o the "." or
"/" prefix. If say I match
>the pattern against "abc/foo" I want to get "foo", not
"/foo". In Perl
>one can simply wrap the "interesting" part in () and get it out of
the
>match. Is it possible to do a similar thing in R?
>
>There seems to be a way to refer to the match, see below, but I couldn't
>figure out how to make gsub return it.
>  
>
>>gsub("[./](*.)", "\\1", "abc/foo")
>>    
>>
>[1] "abcfoo"
>
>
>Thanks,
>Vadim
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>  
>
what about:

gsub(".*[./](*.)", "\\1", "abc/foo")

output-start
[1] "foo"
output-end

or try:

strsplit("abc/foo","/")[[1]][2]

output-start
[1] "foo"
output-end

Peter Wolf