Re: [R] Using grep() to subset lines of text

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Sat, 29 Nov 2008 18:51:07 -0500

grep has a fixed = TRUE argument if you want to ignore all regexp's.

On Sat, Nov 29, 2008 at 3:55 PM, Stavros Macrakis <macrakis_at_alum.mit.edu> wrote:
> Hmm, this brings up an interesting question. What if the string I'm looking
> for contains escape characters? For example, grep( paste( "^", "(ab)" ),
> c("ab","(ab)") ) => c(1), not c(2).
>
> I couldn't find an equivalent to Emacs's regexp-quote, which would let me
> write regexp.quote("(ab)") => "\\(ab\\)". The syntax of regular expressions
> is complicated enough that this is not trivial. Is there perhaps a CRAN
> package with regular expression utilities?
>
> -s
>
> On Sat, Nov 29, 2008 at 7:12 AM, Gabor Grothendieck
> <ggrothendieck_at_gmail.com> wrote:
>>
>> > a <- 2:3
>> > b <- c("aaa 2 aaa", "2 aaa", "3 aaa", "aaa 3 aaa")
>> > re <- paste("^(", paste(a, collapse = "|"), ")", sep = "")
>> > grep(re, b, value = TRUE)
>> [1] "2 aaa" "3 aaa"
>
>



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