[R] get list element names within lapply / sapply call

[David Winsemius]

On Jan 15, 2011, at 5:37 PM, David Winsemius wrote:

>
> On Jan 15, 2011, at 4:06 PM, Jonathan Flowers wrote:
>
>> Hi all,
>>
>> I would like to iterate through a list with named elements and  
>> access the
>> names within an lapply / sapply call. One way to do this is iterate  
>> through
>> the names and index the list with the name.  Is there a way to  
>> iterate
>> through the list elements themselves and access the element names  
>> within in
>> the function? For example,
>>
>> mylist <- list("a"=c(1,2),"b"=c(3,4),"c"=c(5,6))
>> sapply(mylist,function(x){
>> #get name of list elements ("a", "b", "c")
>> #then do other stuff
>> })
>
> You can pass this result to "[[":
> > names(sapply(mylist, names))
> [1] "a" "b" "c"
>
> > sapply( names(sapply(mylist, names)) , function(x) mylist[[x]]^2)
>     a  b  c
> [1,] 1  9 25
> [2,] 4 16 36

Does seem the long way around, though:
 > sapply( mylist, function(x) x^2)
      a  b  c
[1,] 1  9 25
[2,] 4 16 36

>
>
>>
>> Thanks for your suggestions.
>>
>> Jonathan
>>
>> 	[[alternative HTML version deleted]]
>>
>> ______________________________________________
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>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> West Hartford, CT
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT