[R] Apply function to column of array

Warnes, Gregory R gregory_r_warnes at groton.pfizer.com
Tue Oct 29 23:46:02 CET 2002

```Use the 'apply' function.  For information see ?apply.

To plot the density of each column of a matrix, you can do this

mat <- matrix( rnorm(100 * 12), ncol=12 )
par(mfrow=c(3,4))
density.list <- apply( mat, 2, density)
sapply( density.list, plot )

-Greg

> -----Original Message-----
> From: Paul Boutros [mailto:pcboutro at engmail.uwaterloo.ca]
> Sent: Tuesday, October 29, 2002 3:33 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Apply function to column of array
>
>
> 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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