how create a new matrix with values found in an another matrix

Hi, I've the matrix A with dimension (m*n*p). I've found the indexes of the first non-zero elements along the dimension p. They are stored in I with dimension m*n. I would create a new matrix B with dimension m*n with the values corresponding to the indexes I taken in A.

Thanks, Gianluca

[Azzi Abdelmalek]

what if you have'nt n*m non zeros elments, can you explain?

[gianluca]

hi, the matrix A has all zeros except m * n values scattered in the p dimension. The matrix I say me for each row and column (size is m*n) in what page there is the first cell with value different by zero. I would create a new matrix with those values.

Answer 1

[Sven]

Hi Gianluca,

Have you tried using the second output from find_ndim?

[I, Imap] = find_ndim(A,3,'first');
B = A(Imap);  % The actual elements of A that were "found" above, as a vector
B = reshape(B, size(I)); % size(I) is just [m n] from your question

Basically, the elements of the variable I (output from find_ndim) are the subscript references of the 3rd dimension of A. You can also use sub2ind() to get the same result as above, you just also need the first and second subscript references:

[subs2ndDim,subsFirstDim] = meshgrid(1:size(A,2),1:size(A,1));
inds = sub2ind(size(A), subsFirstDim, subs2ndDim, I)
B = A(inds);

Hope this helped you out.