R help - Aug 2003 - filling a matrix who's entries are a function of the indices?

Dear R list,

What's the best way in R to fill a matrix who's entries depend on some
function of the indices?  I'm currently doing:

   Q <- matrix(0, k, k)
   for (A in 1:k) {
      for (B in 1:k) {
         Q[A,B] <- my.function(A,B)
      }
   }

but I wonder if there is a more terse way.

Regards,

Douglas Scofield                 Department of Biology 
d.scofield at umiami.edu            University of Miami
off: (305) 284-3778              P.O. Box 249118
fax: (305) 284-3039              Coral Gables, FL  33124-0421

On 23-Aug-03 Douglas G. Scofield wrote:
> What's the best way in R to fill a matrix who's entries depend on
some
> function of the indices?  I'm currently doing:
> 
>    Q <- matrix(0, k, k)
>    for (A in 1:k) {
>       for (B in 1:k) {
>          Q[A,B] <- my.function(A,B)
>       }
>    }
> 
> but I wonder if there is a more terse way.
Something on the following lines?
> xx<-matrix(rep(c(1,2,3),3),ncol=3)
> xx
     [,1] [,2] [,3]
[1,]    1    1    1
[2,]    2    2    2
[3,]    3    3    3
> yy<-t(xx)
> yy
     [,1] [,2] [,3]
[1,]    1    2    3
[2,]    1    2    3
[3,]    1    2    3
> myfun<-function(XX,YY){(XX-YY)^2}
> myfun(xx,yy)
     [,1] [,2] [,3]
[1,]    0    1    4
[2,]    1    0    1
[3,]    4    1    0

[The above is inspired by the matlab/octave function "meshdom"]

Best wishes,
Ted.


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Date: 23-Aug-03                                       Time: 22:25:07
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