[R] Suggestions for vectorizing/double loop

PIKAL Petr petr.pikal at precheza.cz
Tue Jan 24 08:51:22 CET 2017

Well, your second post is rather confusing too, as is your not reproducible code.

If I understand correctly, you just want to change names of files in a directory according to some rules, which you did not clerly specify.

First I am not sure if R is the best tool for it. Nevertheless, you do not change a contents of any file, just change the name.

I found this with simple answer questioning internet.

Is this what you want?

Here is another possibility

Anyway the concept I would use is.

#read old names

old_names <- list.files(old_path)

#setting new names (you did not explain how do you want to do this)
new_names <- some vector of new names

If order of names is correct
file.rename(old_names, new_names)

othervise it would be needed correctly order both vectors before file.rename.

The crucial information is how do you want set the new names vector. You shold specify it by reproducible way if you want more precise answer.

Copying files is in this case best done by OS itself.


> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Luanna
> Dixson
> Sent: Monday, January 23, 2017 6:39 PM
> To: r-help at r-project.org
> Subject: Re: [R] Suggestions for vectorizing/double loop
> Hi all,
> Thanks very much for your help! You are correct in thinking the list is the
> same as before, actually, my question was more about how to do the next
> steps, where I needed to match the filenames of the files in my directory
> with old (i.e current) and new file name prefixes in my list. For each match I
> then wanted to rename the original file using the corresponding new
> filename prefix from the list.
> Sorry for being a bit confusing, I didn't post my first attempt to do this at first
> as my code just didn't work at all, but I have had another go using a matrix
> instead and I think this does the job.
> old_path="./old/"
> new_path="./new/"
> old_names <- list.files(old_path)
> head(old_names)
> oldnames=c('1002', '1003')
> newnames=c('1002_new', '1003_new')
> mapping=cbind(oldnames,newnames)
> head(mapping)
> for (i in old_names){
>     temp <- unlist(strsplit(i, "[.]"))[1]
>     n <- which(is.element(mapping,temp))
>     if(length(n)>0) {
>         #copy the file to the new folder
>         #re name it and the name is paste(mapping[n,2], '.xls', sep="")
>         print(paste(mapping[n,2], '.xls', sep=""))
>         newnames <- paste(mapping[n,2], '.xls', sep="")
>         file.copy(from = paste(old_path, i, sep=""),
>                   to = paste(new_path, newnames))
>     }
> }
> On 23 January 2017 at 13:28, Luanna Dixson
> <justanotherdigression at gmail.com>
> wrote:
> > I need to rename a bunch of files, by searching for string matches in
> > a list. Each list element containings a character with the old
> > filename that I want to match to, and the new file name that I want to
> rename by.
> >
> > For instance, here filename '1001.xls' should match to
> > list[[1]]$oldname and I want to rename it to 'newa.xls' from
> list[[1]]$newname.
> >
> > The actual new file names I have will feature a random alphanumeric
> > number and the list will have a length of ~600.
> >
> >
> > # files I want to rename
> >
> > files with old file name =c('1001.xls', '1002.xls')
> >
> > # list with old file names and new file names
> >
> > oldnames=c('1001', '1002', '1003')
> >
> > newnames=c('newa', 'newb', 'newc')
> >
> > df=data.frame(oldnames,newnames)
> >
> > list <- split(df, rownames(df))
> >
> >
> > # turn list elements in character
> >
> > for(i in 1:length(list)) list[[i]]$oldnames=as.
> > character(list[[i]]$oldnames)
> >
> > for(i in 1:length(list)) list[[i]]$newnames=as.
> > character(list[[i]]$newnames)
> >
> >
> > I heard that it would be better to vectorize this than trying to do a
> > double loop so if someone could give me a hint about how to do this I
> > would be very grateful!
> >
>       [[alternative HTML version deleted]]
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.

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