Using array values as indices for inserting values into a larger destination array

Hello all,

I have 3 arrays, one containing row indices, one containing column indices, and one containing the corresponding value at the matching row and column location.

I am trying to use the indices arrays to place the corresponding values into a larger array at the locations specified by the row and column indices arrays.

Here is a simplified example:

rowIndices = magic(8);

colIndices = magic(8);

values = 1:8;

values = repmat(values',1,8);

destinationArray = zeros(max(rowIndices(:)),max(colIndices(:)));

Basically, values(1,1) should be placed into destinationArray at rowIndices(1,1), colIndices(1,1) but for all (row,col,val) combinations at once.

I am using a quite large dataset and am trying to avoid loops whenever possible so I was hoping there is an efficient way to do this with a limited number of operations.

Thank you for your time and if you can help I'll acknowledge you in my dissertation!

-Chris H.

[Stephen23]

Note that both magic calls will return the same output matrix, so your example will only allocate data to the diagonal of the destination matrix.

Answer 1

[Stephen23]

Use sub2ind:

N = 8;
R = randi(9,N); % more interesting than MAGIC.
C = randi(9,N); % more interesting than MAGIC.
V = reshape(1:N*N,N,N); % non-repeating example values.
S = [max(R(:)),max(C(:))];
Z = zeros(S);
Z(sub2ind(S,R,C)) = V

[Christopher]

This is exactly what I was looking for, thank you so much for the solution and the helpful testing comments!!!!