[R] regular expression

[Bernd Weiss]

Am 31.03.2011 21:06, schrieb array chip:
> Ok then this code didn't do what I wanted. I want "not including
> 'arg' before '.symptom'", not individual letters of "arg", but rather
> as a word.
>
> Bill Dunlap suggested using invert=T, it works for single 1
> condition, but not for 2 conditions here: not including "arg" before
> ".", but at the same time, does include ".symptom".
>
> Any other suggestions would be appreciated

This does work (but I am by no means an expert in regex...). I am using 
'negative lookbehind'[1] to define an expression like 'arg'.

 > grep('(?<!(arg))\\.symptom',"arg.symptom",value=T, perl = T)
character(0)

 > grep('(?<!(arg))\\.symptom',"liver.symptom",value=T, perl = T)
[1] "liver.symptom"

Bernd

[1] http://www.regular-expressions.info/lookaround.html