[R] regular expression

Bernd Weiss bernd.weiss at uni-koeln.de
Fri Apr 1 03:19:25 CEST 2011

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)

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


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

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