Extract 3rd Dimension values of a Matrix using sub2ind

A is a Matrix of size 15x12x480

ii = size 13x1 (specific row numbers) e.g. [6,7,8,10,12.....]

jj = size 13x1 (specific column numbers) e.g. [2,4,6,9,11.....]

I want to extract the values of A matrix for ii,jj locations upto 3 rd dimension

%%% THE CODE ISN'T WORKING
Extract_A = A(sub2ind(size(A), ii(:,1),jj(:,1),:));

Anyone has a solution?

Thanks in advance

Answer 1

[Walter Roberson]

sub2ind() does not accept ':' as an input: it only accepts numbers.

The subscript vectors you pass must all be the same size as well.

If you want the combination of all rows listed in ii with all columns listed in jj with all 480 pages, then you would just use

A(ii, jj, :)

If what you are trying to do is like

cat(4, A(ii(1), jj(1), :), A(ii(2), jj(2), :), A(ii(3), jj(3), :), ...)

producing a 1 x 1 x 480 x 13 array, then you will need to repmat() the ii and jj .

Another approach:

szA = size(A);
page_bases = sub2ind(szA, ii, jj, ones(size(ii)));
pagesize = prod(szA(1:end-1));
pageoffsets = (0:szA(end)-1).'.*pagesize;
B = A(page_bases + pageoffsets);

B would be size(A,3) x length(ii)