[R] grep for multiple pattern?

[Prof Brian Ripley]

On 13/02/2014 16:25, Rainer M Krug wrote:
>
> On 02/13/14, 17:23 , jim holtman wrote:
>> use the "|" in regular expressions:
>>
>>   grep(c("an|em|eb", month.name <http://month.name/>)
>
> Thanks - again a reason to learn regexp.

Note though that is an *extended* regex.  They are the default in R, but 
not for grep, sed, ....

Another thing to watch out is that GNU grep allows (a\|b\|c) in 'basic' 
regexps -- but the POSIX standard does not, and nor do other 
implementations.  The authors of the graphviz configure code (shipped 
with Rgraphviz) did not know this and wasted other people's resources.

>
> Cheers,
>
> Rainer
>
>>
>>
>> Jim Holtman
>> Data Munger Guru
>>
>> What is the problem that you are trying to solve?
>> Tell me what you want to do, not how you want to do it.
>>
>>
>> On Thu, Feb 13, 2014 at 9:43 AM, Rainer M Krug <Rainer at krugs.de
>> <mailto:Rainer at krugs.de>> wrote:
>>
>>      Hi
>>
>>      I want to search for multiple pattern as grep is doing for a single
>>      pattern, but this obviously not work:
>>
>>      > grep("an", month.name <http://month.name>)
>>      [1] 1
>>      > grep("em", month.name <http://month.name>)
>>      [1]  9 11 12
>>      > grep("eb", month.name <http://month.name>)
>>      [1] 2
>>      > grep(c("an", "em", "eb"), month.name <http://month.name>)
>>      [1] 1
>>      Warning message:
>>      In grep(c("an", "em", "eb"), month.name <http://month.name>) :
>>        argument 'pattern' has length > 1 and only the first element will
>>      be used
>>      >
>>
>>      Is there an equivalent which returns the positions as grep is doing, but
>>      not using the strict full-string matching of match()?
>>
>>      I could obviously do:
>>
>>      > unlist( sapply(pat, grep, month.name <http://month.name> ) )
>>       an em1 em2 em3  eb
>>        1   9  11  12   2
>>
>>      but is there a more compact command I am missing?
>>
>>      Thanks,
>>
>>      Rainer
>>
>>      --
>>      Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
>>      Biology, UCT), Dipl. Phys. (Germany)
>>
>>      Centre of Excellence for Invasion Biology
>>      Stellenbosch University
>>      South Africa
>>
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>>
>>      email:      Rainer at krugs.de <mailto:Rainer at krugs.de>
>>
>>      Skype:      RMkrug
>>
>>
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>>
>>
>
>
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
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