[R] Apply function to column of array

[Warnes, Gregory R]

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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