Great. thank you Bernd! Learned a new thing here.

John




________________________________
From: Bernd Weiss <bernd.weiss@uni-koeln.de>

Cc: r-help@r-project.org
Sent: Thu, March 31, 2011 6:19:25 PM
Subject: Re: [R] regular expression

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

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