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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