Avoid for loop on sum on given indexes, use accumarray?

Hi,

I'm trying to get rid of the for loop on the follwoing code:

S=zeros(100,50);
V=rand(1,50);
Index=round(50*rand(1,50))
for i=1:50
S(:,Index(i))=S(:,Index(i))+V(i);
end

I probably need to use accumarray but I cannot figure how.

Thanks a lot

[Walter Roberson]

Why are you creating 100 rows when you do the same thing to all of them? Why not create one row with the values and later replicate to 100 copies?

[Lenaic Couedel]

It is a simplified version of my problem.

A more accurate one would be:

S=zeros(100,50);
V=rand(100,50);
Index=round(50*rand(1,50))
for i=1:50
    S(:,Index(i))=S(:,Index(i))+V(:,i);
end

Thanks

Answer 1

[Walter Roberson]

Idx1 = repmat(1:size(V,1), 1, length(Index)) ;
Idx2 = repelem(Index, 1, size(V, 1));
S = accumarray([Idx1(:), Idx2(:)], V(:), size(V)) ;

[Lenaic Couedel]

Great,

Thanks