3D Matrix indexing from a vector

Hi,

If one puts a matrix of indices I to a vector A (e.g,: A(I)) one would get an output with the size of I filled with the values of A in the location given by I. Now, suppose A is now a matrix itself, and I want the above procedure to be applied to each row of A individually, placing each output matrix in a different page of a resultant 3D array.

Here is a sample code that works using a loop:

A=[ 1  2  3  4  5  6  7  8  9  0;...  % values
   11 12 13 14 15 16 17 18 19 20;...
   21 22 23 24 25 26 27 28 29 30;...
   31 32 33 34 35 36 37 38 39 40;...
   41 42 43 44 45 46 47 48 49 50];
I=[7 8 5 7 9 5 6 7 8 9;...  indices
   2 3 1 4 3 1 4 2 3 1];
% Build Acube
for i=1:size(A,1)
    tmp=A(i,:);
    Acube(:,:,i)=tmp(I);
end;

The question is: how can you vectorize it? (I note I used "large" (>=5) values for the first row of I, and "small" values (<5) for the second row to ease debugging - but any value between 1 and size(A,2) should work).

Answer 1

[Matt J]

    [m,n]=size(I);

    Acube=reshape(A(:,I).',m,n,[]),