R help - May 2010 - excluding on element from a list

Dear List,

I am making a list of all the files in a folder and I want to exclude
one file called "proj.current".  This is the 31st file in a folder.
Currently I use the command:

tdirs <- list.files(pattern="proj.")[-31]

However I would like to exclude it based on its name and not the position.

Any advice would be useful.

Thanks,
Daisy



Daisy Englert Duursma

Room E8C156
Dept. Biological Sciences
Macquarie University  NSW  2109
Australia

On 05/24/2010 05:40 PM, Daisy Englert Duursma wrote:
> Dear List,
>
> I am making a list of all the files in a folder and I want to exclude
> one file called "proj.current".  This is the 31st file in a
folder.
> Currently I use the command:
>
> tdirs<- list.files(pattern="proj.")[-31]
>
> However I would like to exclude it based on its name and not the position.
>
Hi Daisy,
I think that:

file_list<-list.files(pattern="proj[.]")
tdirs<-file_list[!as.logical(match(file_list,"proj.current",0))]

should do the trick.

Jim

Thanks for your help and for the info on the website. I did not know
what to call regular expressions and so I could not search for them.
Cheers!
d

On Mon, May 24, 2010 at 7:08 PM,  <Richard.Cotton at hsl.gov.uk>
wrote:
>> I am making a list of all the files in a folder and I want to exclude
>> one file called "proj.current". ?This is the 31st file in a
folder.
>> Currently I use the command:
>>
>> tdirs <- list.files(pattern="proj.")[-31]
>>
>> However I would like to exclude it based on its name and not the
> position.
>
> You need to update the pattern in the regular expression to look for
> strings beginning with "proj.", but not having
"current" afterwards.
>
> My first thought was to use perl style regular expressions, but apprently
> this isn't supported.
> tdirs <- list.files(pattern = "proj\\.(?!current)", perl=TRUE)
? #Throws
> error
>
> Instead, you're probably better off doing it in two steps.
> tdirs <- list.files(pattern="proj\\.")
> tdirs <- tdirs[tdirs != "proj.current"]
>
> Notice the difference between "proj." and "proj\\.".
?The first means
> 'proj followed by any character', and the second means 'proj
followed by a
> dot'. ?See http://www.regular-expressions.info/quickstart.html for more
> info on regexes.
>
> Regards,
> Richie.
>
> Mathematical Sciences Unit
> HSL
>
>
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-- 
Daisy Englert Duursma

Room E8C156
Dept. Biological Sciences
Macquarie University  NSW  2109
Australia

Tel +61 2 9850 9256



10A Carrington Rd
Hornsby, NSW 2077

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