R help - Nov 2002 - Regular Expressionsionism

Isn't there a cryptic footnote somewhere in the blue book that describes
regular expressions as "a funny little language ..." ?  Well, I'm
not laughing!

I've googled and Man paged, but the GREP-style solution to the following
problem still eludes me:

... Using a regular expression in the "pattern" argument to
list.files() to restrict the return to filenames which
contain both "Elstim" and "post".  E.g.,
>list.files()
... 
[133] "J30710_Control_msa_amplitude_5_25_s1-30w.pre"
[134] "J30710_Elstim_msa_amplitude_5_25_s1-30w.post"
[135] "J30710_Elstim_msa_amplitude_5_25_s1-30w.pre"
[136] "J30712_Control_msa_amplitude_5_25_s1-41_44-46_48w.post"
[137] "J30712_Control_msa_amplitude_5_25_s1-41_44-46_48w.pre"
[138] "J30712_Elstim_msa_amplitude_5_25_s1-17_19-43_45_48w.post"
                                       
I have not found the key to generating the logical AND equivalent of the
"|" OR infix operator, a
proxy for the simpleton's dream:  my.list.files(pattern="*Elstim"
& "*post")

Thanks

- Derek

P.S.,

Of course I could always do this in stages:
>  elstims <- list.files(pattern = "Elstim")  # all the files
with "Elstim"
>  ElPostinos <- grep("post",elstims) # all the elstim files
with "post"
>  my.file.list <- elstims[ElPostinos]  # result:  list of filenames 
But my conscience would bother me for taking the easy way out.






Derek N. Eder
G?teborgs Universitet
Institutionen f?r klinisk neurovetenskap
Klinisk Neurofysiologi
Sahlgrenska universitetssjukhuset SS/SU
Bl? str?ket 7, v?n 3
SE 413 45  G?teborg
Sverige
Tlf. +46 (031) 34  244 14  (office)   NYTT!
Tlf. +46 (031) 34 212 83  (laboratory)
Tlf. +46 0709 / 7 212 83 (mobil)
Fax. +46 (031) 82 81 63 
derek.eder at neuro.gu.se


Gothenburg University
Institute of Clinical Neuroscience,
Department of Clinical Neurophysiology
Salhgrenska Hospital  SU/SS
SE 413 45  G?teborg
Sweden



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"Derek Eder" <Derek.Eder at neuro.gu.se> writes:
> Isn't there a cryptic footnote somewhere in the blue book that
describes regular expressions as "a funny little language ..." ? 
Well, I'm not laughing!
> 
> I've googled and Man paged, but the GREP-style solution to the
following problem still eludes me:
> 
> ... Using a regular expression in the "pattern" argument to
list.files() to restrict the return to filenames which
> contain both "Elstim" and "post".  E.g.,
> 
> >list.files()
> ... 
> [133] "J30710_Control_msa_amplitude_5_25_s1-30w.pre"
> [134] "J30710_Elstim_msa_amplitude_5_25_s1-30w.post"
> [135] "J30710_Elstim_msa_amplitude_5_25_s1-30w.pre"
> [136] "J30712_Control_msa_amplitude_5_25_s1-41_44-46_48w.post"
> [137] "J30712_Control_msa_amplitude_5_25_s1-41_44-46_48w.pre"
> [138] "J30712_Elstim_msa_amplitude_5_25_s1-17_19-43_45_48w.post"
>                                        
> I have not found the key to generating the logical AND equivalent of the
"|" OR infix operator, a
> proxy for the simpleton's dream: 
my.list.files(pattern="*Elstim" & "*post")
As long a you know the order, how about "Elstim.*post" ?

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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> "Derek Eder" <Derek.Eder at neuro.gu.se> writes:
..
> > ... Using a regular expression in the "pattern" argument to 
> > list.files() to restrict the return to filenames which
> > contain both "Elstim" and "post".  E.g.,
> > 
> > >list.files()
> > ... 
> > [133] "J30710_Control_msa_amplitude_5_25_s1-
30w.pre"                                    
               
> > [134] "J30710_Elstim_msa_amplitude_5_25_s1-
30w.post"                                    
               
> > [135] "J30710_Elstim_msa_amplitude_5_25_s1-
30w.pre"                                     
               
> > [136] "J30712_Control_msa_amplitude_5_25_s1-41_44-
46_48w.post"                          
               
> > [137] "J30712_Control_msa_amplitude_5_25_s1-41_44-
46_48w.pre"                           
               
> > [138] "J30712_Elstim_msa_amplitude_5_25_s1-17_19-
43_45_48w.post"                        
               
> >                                        
> > I have not found the key to generating the logical AND equivalent of 
the "|" OR infix
operator, a 
> > proxy for the simpleton's dream: 
my.list.files(pattern="*Elstim"
& "*post") 

In this case, the quick and (very) dirty method I'd also use is:

grep("Elstim",grep("post",list.files()))

generalising that via recursion to match an arbitrary number of REs 
and "&" and "|" operators is left as an excercise.... 

Cheers

Jason

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