[R] Apply function to column of array

[Roger Peng]

It seems that for this you may in fact want to use a loop.  If you have a
matrix with p columns (say it's called 'm'), then you might consider:

results <- vector("list", length = p)
for(i in 1:p) results[[i]] <- density(m[,i])

If you want to use lapply() then something like the following should work:

results <- lapply(1:p, function(i) density(m[,i]))

Then 'results' is a vector of lists which contain the results to the
individual calls to density().  You can then cycle over this vector to
make your plots or whatever.

-roger
_______________________________
UCLA Department of Statistics
rpeng at stat.ucla.edu
http://www.stat.ucla.edu/~rpeng

On Tue, 29 Oct 2002, Paul Boutros wrote:

> Hi all,
> 
> I would like to apply a function to each column of an 2-dimensional array,
> and store the result in a new 1-dimensional vector.  I am not sure how to
> go about doing that syntatically.  For instance, can I use lapply?  And,
> if so, how do I specify which dimension should be used?  Also, how do I
> pre-specify the type of object that will go into the 1-dimensional vector.
> 
> I'm not sure if it is important, the function I wish to apply to the
> columns is density().  Additionally, I wish to be able to take these
> density objects (stored in that 1-dim vector) and place them onto a
> multiple-figure environment.
> 
> I'm new with R, so I tend to think in loops.  I'd appreciate any guidance
> or tips on better ways to handle this problem.
> 
> Thanks!
> Paul
> 
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