[R] Suggestions for vectorizing/double loop

[Michael Dewey]

Dear Luanna

It is not compulsory to avoid for loops but see below

On 23/01/2017 12:28, Luanna Dixson 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))
>

Both df and list are already in existience and you are overwriting them. 
It is best practice not to do that.
>
> # turn list elements in character
>
> for(i in 1:length(list)) list[[i]]$oldnames=as.character(list[[i]]$oldnames)
>

Something like

lapply(list, function(x) x$oldnames <- as.character(x$oldnames))

would probably work.
You might want sapply instead of lapply

> 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!
>
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>
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-- 
Michael
http://www.dewey.myzen.co.uk/home.html