[R] regular exprs

[Gabor Grothendieck]

On Sun, Nov 7, 2010 at 10:15 AM, Dimitris Rizopoulos
<d.rizopoulos at erasmusmc.nl> wrote:
> Dear All,
>
> I would appreciate any help with the following: given the vector 'x'
>
> x <- c("Ass1", "Ass.s1", "Ass2", "Ass.s2")
>
> I would like to pick up the positions where the character string contains
> "Ass" but does not contain "Ass.s", so for 'x' that would be positions 1 and
> 3.
>
> I guess this could be programmed around grep() using a suitable regular
> expression, but I haven't managed to succeed.
>

Assuming that "Ass" appears at most once in each string, as in the example:

> x <- c("Ass1", "Ass.s1", "Ass2", "Ass.s2", "Ass.")
> grep("Ass(?![.]s)", x, perl = TRUE)
[1] 1 3 5

See ?regex for more info.  There is also regular expression links in
the Links box at http://gsubfn.googlecode.com .

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