R help - Dec 2015 - Applying a function to a matrix using indexes as arguments

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.

Thanks a lot for your suggestions.
Matteo

	[[alternative HTML version deleted]]

This calculation divides by values centered around zero.  The only context that
I can think of that would require such silliness is a homework problem, and this
list has a no-homework policy. If not, then mentioning the theory you are
applying might help someone point you at an existing function that achieves your
goals while avoiding divide-by-zero errors.

Since you also posted in HTML I gather that you have not read the Posting Guide
mentioned below.  Avoiding HTML on this list is to your benefit,  since using it
inevitably leads to others seeing a garbled version of what you sent. Please
read the PG for more important guidance.
-- 
Sent from my phone. Please excuse my brevity.

On December 16, 2015 4:18:56 PM PST, 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.
>
>Thanks a lot for your suggestions.
>Matteo
>
>	[[alternative HTML version deleted]]
>
>______________________________________________
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.
	[[alternative HTML version deleted]]

> 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]]
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius
Alameda, CA, USA

> On Dec 16, 2015, at 5:34 PM, David Winsemius <dwinsemius at
comcast.net> wrote:
> 
> 
>> 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.
Furthermore, you can neatly populate the W matrix with the `[<-` function:

 W[] <- mapply( function( i,j,fac) {fac*A[i]*B[j]/C[i,j]}, 
                i=row(W), j=col(W),MoreArgs=list(fac=10) )
> W
          [,1]      [,2]      [,3]
[1,] -86207.97 -135764.4 -142509.4
[2,] 325768.16 -913037.0  243715.7
> 
> -- 
> David.
>> 
>> Thanks a lot for your suggestions.
>> Matteo
>> 
>> 	[[alternative HTML version deleted]]
>> 
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
> 
> David Winsemius
> Alameda, CA, USA
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius
Alameda, CA, USA