[R] Applying a function to a matrix using indexes as arguments
David Winsemius
dwinsemius at comcast.net
Thu Dec 17 02:34:01 CET 2015
> On Dec 16, 2015, at 4:18 PM, Matteo Richiardi <matteo.richiardi at gmail.com> wrote:
>
> I have to evolve each element of a matrix W
>
> W <- matrix(0,2,3)
>
> according to some function which uses the indices of the matrix [i,j] as
> arguments:
> w.fun = function(i,j) {
> return A[i]*B[j]/(C[i,j])
> }
>
> where
> A<-c(100,100)
> B<-c(200,200,200)
> C <- matrix( rnorm(6,mean=0,sd=1), 2, 3)
>
> How can I do it, without recurring to a loop? Also, in my application I
> need to pass the function another argument.
mapply( function( i,j,fac) {fac*A[i]*B[j]/C[i,j]},
i=row(W),
j=col(W),
MoreArgs=list(fac=10) )
[1] -86207.97 325768.16 -135764.41 -913036.95 -142509.39
[6] 243715.67
N.B. all of the *apply functions are really loops.
--
David.
>
> Thanks a lot for your suggestions.
> Matteo
>
> [[alternative HTML version deleted]]
>
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David Winsemius
Alameda, CA, USA
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