[R] Regex for Special Characters under Grep

[Henrik Bengtsson]

A regular set is given by "[<set>]".  The complementary set is given
by "[^<set>]" where <set> is a set of symbols.  I don't think you have
to escape symbols in <set> (but I might be wrong).  In any case, this
does what you want:

> lines <- c("abc", "!abc", "#abc", "^abc", " #abc")
> pattern <- "^[^!#^]";
> grep(pattern, lines, value=TRUE)
[1] "abc"   " #abc"

/Henrik


On Thu, Jun 12, 2008 at 8:06 PM, Marc Schwartz
<marc_schwartz at comcast.net> wrote:
> on 06/12/2008 08:42 PM Gundala Viswanath wrote:
>>
>> Hi all,
>>
>> I am trying to capture lines of a file that DO NOT
>> start with the following header: !, #, ^
>>
>> But somehow my regex used under grep doesn't
>> work.
>>
>> Please advice what's wrong with my code below.
>>
>> __BEGIN__
>> in_fname <- paste("mydata.txt,".soft",sep="")
>> data_for_R <- paste("data_for_R/", args[3], ".softR", sep="")
>>
>> # my regex construction
>> cat(temp[-grep("^[\^\!\#]",temp,perl=TRUE)], file=data_for_R, sep="\n")
>>
>>
>> dat <- read.table(data_for_R)
>> ___END__
>>
>
> You need to double the escape character when being used to differentiate
> meta-characters in a regex. Note also that the only meta-character in your
> sequence is the carat ('^').
>
> Lines <- c("! Not This Line", "# Not This Line", "^ Not This Line",
>           "This Line")
>
>> Lines
> [1] "! Not This Line" "# Not This Line" "^ Not This Line"
> [4] "This Line"
>
>> grep("^[!#\\^]", Lines)
> [1] 1 2 3
>
>> Lines[-grep("^[!#\\^]", Lines)]
> [1] "This Line"
>
>
> HTH,
>
> Marc Schwartz
>
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