[R] access list component names with lapply

Prof Brian Ripley ripley at stats.ox.ac.uk
Thu Mar 30 10:23:46 CEST 2006

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.


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

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