R help - Mar 2006 - access list component names with lapply

I have a question regarding accessing the names of list
components when applying a function with lapply.

Here is an example that demonstrates what I'd like to do.

I have a list like this one:
	
	mylist <- list(a=letters[1:10], b=letters[10:1], c=letters[1:3])

Now I would like to append the names of the list components to their
corresponding vectors with the c() function. I thought this could
be done like in the following command, but it doesn't:

	lapply(mylist, function(x) { c(names(x), x)  } )

I know how to do this in a for loop, but lapply runs so much faster over
large lists.
	
Any help on this simple problem will be highly appreciated.

Thomas


-- 
Thomas Girke
1008 Noel T. Keen Hall
University of California
Riverside, CA 92521

Ph: 951-827-2469
Fax: 951-827-4437

Try this:

lapply(names(mylist), function(nm) c(nm, mylist[[nm]]))

On 3/29/06, Thomas Girke <thomas.girke at ucr.edu>
wrote:
> I have a question regarding accessing the names of list
> components when applying a function with lapply.
>
> Here is an example that demonstrates what I'd like to do.
>
> I have a list like this one:
>
>        mylist <- list(a=letters[1:10], b=letters[10:1], c=letters[1:3])
>
> Now I would like to append the names of the list components to their
> corresponding vectors with the c() function. I thought this could
> be done like in the following command, but it doesn't:
>
>        lapply(mylist, function(x) { c(names(x), x)  } )
>
> I know how to do this in a for loop, but lapply runs so much faster over
> large lists.
>
> Any help on this simple problem will be highly appreciated.
>
> Thomas
>
>
> --
> Thomas Girke
> 1008 Noel T. Keen Hall
> University of California
> Riverside, CA 92521
>
> Ph: 951-827-2469
> Fax: 951-827-4437
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>

On Wed, 29 Mar 2006, Thomas Girke wrote:
> I have a question regarding accessing the names of list
> components when applying a function with lapply.
>
> Here is an example that demonstrates what I'd like to do.
>
> I have a list like this one:
>
> 	mylist <- list(a=letters[1:10], b=letters[10:1], c=letters[1:3])
>
> Now I would like to append the names of the list components to their
> corresponding vectors with the c() function. I thought this could
> be done like in the following command, but it doesn't:
>
> 	lapply(mylist, function(x) { c(names(x), x)  } )
>
> I know how to do this in a for loop, but lapply runs so much faster over
> large lists.
Try

lapply(names(mylist), function(x) c(x, mylist[[x]]))

(that prepends, but your code attempts to prepend rather than append so I
am guessing that it what you wanted).


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

Thomas Girke wrote:
> I have a question regarding accessing the names of list
> components when applying a function with lapply.
> 
> Here is an example that demonstrates what I'd like to do.
> 
> I have a list like this one:
> 	
> 	mylist <- list(a=letters[1:10], b=letters[10:1], c=letters[1:3])
This is how I am doing this:
mapply(functuion(x,y)myfun(x, y),x, names(x)))

Kjetil
> 
> Now I would like to append the names of the list components to their
> corresponding vectors with the c() function. I thought this could
> be done like in the following command, but it doesn't:
> 
> 	lapply(mylist, function(x) { c(names(x), x)  } )
> 
> I know how to do this in a for loop, but lapply runs so much faster over
> large lists.
> 	
> Any help on this simple problem will be highly appreciated.
> 
> Thomas
> 
>