R help - Apr 2011 - Extract information from the names of a list within lapply

Dear list,

I want to loop over a list through lapply and at the same time I want to
extract some information from the names of the list elements. lapply does
not seem to carry the names. Is there anyway to access the names of a list
within lapply? Thanks.

Jun

	[[alternative HTML version deleted]]

Hi Jun,

On Fri, Apr 15, 2011 at 11:14 AM, Jun Shen <jun.shen.ut at gmail.com>
wrote:
> Dear list,
>
> I want to loop over a list through lapply and at the same time I want to
> extract some information from the names of the list elements. lapply does
> not seem to carry the names. Is there anyway to access the names of a list
> within lapply? Thanks.
Not in the way you are probably trying to do it, but consider:

## 1 (what you are probably doing)
lapply(mtcars, mean)
## 2 (an alternative)
lapply(colnames(mtcars), function(x) {cat(x, fill = TRUE); mean(mtcars[, x])})

The main downside of #2 is that it takes more code, and the resulting
output is not named.  However, it gives you all the flexibility you
need.

HTH,

Josh

>
> Jun
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> 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.
>


-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/

Try this:

lapply(mtcars, function(.)names(mtcars)[match.call()[[2]][[3]]])

On Fri, Apr 15, 2011 at 3:14 PM, Jun Shen <jun.shen.ut at gmail.com>
wrote:
> Dear list,
>
> I want to loop over a list through lapply and at the same time I want to
> extract some information from the names of the list elements. lapply does
> not seem to carry the names. Is there anyway to access the names of a list
> within lapply? Thanks.
>
> Jun
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> 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.
>


-- 
Henrique Dallazuanna
Curitiba-Paran?-Brasil
25? 25' 40" S 49? 16' 22" O