[R] Applying a function to a matrix using indexes as arguments

[David Winsemius]

> 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
> 
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> 
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David Winsemius
Alameda, CA, USA