Assignment and indexing issue

I have some data and their indexed coordinates in an array x :

 % x(q,:) == [jq,iq,kq,xq]

I have an empty 3D matrix d in which I want to store these data, like so :

 d = Inf(m,n,p);
 for i=1:length(x)
     d(x(i,2),x(i,1),x(i,3)) = x(i,4);
 end

My question is, is there any way to do it without a loop ? I was thinking something like this but it does not work :

 d = Inf(m,n,p);
 d(x(:,[2,1,3])) = x(:,4);

Maybe throw a sub2ind or something in there somewhere ?..

Answer 1

[Walter Roberson]

d = accumarray(x(:,[2 1 3]), x(:,4), [m, n, p]);

[Marsellus Wallace]

Arf, I've mastered bsxfun but accumarray still eludes me... Thanks !

Answer 2

[Jos (10584)]

x = [1 1 1 10 ; 1 1 2 20 ; 2 3 2 30] % data

sz = max(x(:,1:3),[],1)
d = Inf(sz)
idx = sub2ind(sz,x(:,1),x(:,2),x(:,3)) 
d(idx) = x(:,4)

[Marsellus Wallace]

What would be best between using sub2ind and accumarray (other answer) ?

[Jos (10584)]

Both are fine. Compare them for readability, your understanding of the code, speed of execution, translation into other languages, etc.

[Marsellus Wallace]

Well, I prefer sub2ind for readability but accumarray for conciseness. I'll test tomorrow for speed of execution but it was pretty quick already even with the loop, so...

Anyway, thanks !