Monica Pisica wrote:
> Hi everybody,
>
> Thank you for the suggestions and especially the explanation Waclaw provided
> for his code. Maybe one day i will be able to wrap my head around this.
>
> Thanks again,
>
you're welcome. note that if efficiency is an issue, you'd better have
perl=TRUE there:
output = sub('.*//(.*)[.]tif$', '\\1', input, perl=TRUE)
with perl=TRUE, the one-pass solution is somewhat faster than the
two-pass solution of gabor's -- which, however, is probably easier to
understand; with perl=FALSE (the default), the performance drops:
strings = sprintf(
'f:/foo/bar//%s.tif',
replicate(1000, paste(sample(letters, 10), collapse='')))
library(rbenchmark)
benchmark(columns=c('test', 'elapsed'), replications=1000, order=NULL,
'one-pass, perl'=sub('.*//(.*)[.]tif$', '\\1', strings, perl=TRUE),
'two-pass, perl'=sub('.tif$', '', basename(strings), perl=TRUE),
'one-pass, no perl'=sub('.*//(.*)[.]tif$', '\\1', strings,
perl=FALSE),
'two-pass, no perl'=sub('.tif$', '', basename(strings), perl=FALSE))
# 1 one-pass, perl 3.391
# 2 two-pass, perl 4.944
# 3 one-pass, no perl 18.836
# 4 two-pass, no perl 5.191
vQ
>
> Monica
>
> ----------------------------------------
>
>> Date: Tue, 26 May 2009 15:46:21 +0200
>> From: waclaw.marcin.kusnierc...@idi.ntnu.no
>> To: pisican...@hotmail.com
>> CC: r-help@r-project.org
>> Subject: Re: [R] split strings
>>
>> Monica Pisica wrote:
>>
>>> Hi everybody,
>>>
>>> I have a vector of characters and i would like to extract certain parts. My
>>> vector is named metr_list:
>>>
>>> [1] "F:/Naval_Live_Oaks/2005/data//BE.tif"
>>> [2] "F:/Naval_Live_Oaks/2005/data//CH.tif"
>>> [3] "F:/Naval_Live_Oaks/2005/data//CRR.tif"
>>> [4] "F:/Naval_Live_Oaks/2005/data//HOME.tif"
>>>
>>> And i would like to extract BE, CH, CRR, and HOME in a different vector
>>> named "names.id"
>>>
>> one way that seems reasonable is to use sub:
>>
>> output = sub('.*//(.*)[.]tif$', '\\1', input)
>>
>> which says 'from each string remember the substring between the
>> rigthmost two slashes and a .tif extension, exclusive, and replace the
>> whole thing with the captured part'. if the pattern does not match, you
>> get the original input:
>>
>> sub('.*//(.*)[.]tif$', '\\1', 'f:/foo/bar//buz.tif')
>> # buz
>>
>> vQ
>>
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