Hello,
Try
K <- array(0,dim=c(2,2,2,2)) #dimensions will be much larger
for(x1 in 1:2){
for(y1 in 1:2) {
for(x2 in 1:2) {
for(y2 in 1:2) {
K[x1,y1,x2,y2] <- x1*y2 - sin(x2*y1) #this is just a dummy
function.
}
}
}
}
fun <- function(x){
x1 <- x[1] # these are
x2 <- x[2] # not
y1 <- x[3] # really
y2 <- x[4] # needed
x1*y2 - sin(x2*y1) # could have used x[1], etc
}
res <- apply(expand.grid(1:2, 1:2, 1:2, 1:2), 1, fun)
dim(res) <- c(2, 2, 2, 2)
res
all.equal(K, res)
[1] TRUE
See the help pages
?expand.grid
?apply
Hope this helps,
Rui Barradas
math_daddy wrote
>
> Hello. I have a 4 dimensional array and I want to fill in the slots with
> values which are a function of the inputs. Through searching the forums
> here I found that the function "outer" is helpful for 2x2 matrices but
> cannot be applied to general multidimensional arrays. Is there anything
> which can achieve, more efficiently than the following code, the job I
> want?
>
> K <- array(0,dim=c(2,2,2,2)) #dimensions will be much larger
> for(x1 in 1:2)
> {
> for(y1 in 1:2)
> {
> for(x2 in 1:2)
> {
> for(y2 in 1:2)
> {
> K[x1,y1,x2,y2] <- x1*y2 - sin(x2*y1) #this is just a dummy
> function.
> }
> }
> }
> }
>
> Thank you in advance for any help.
>
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