subtracting a value from the first positive element

hi all I have this problem: let's say I have large array and I want to subtract the first positive value that apperas (in each column) from a particular number. But only the first one, how can i do it?

thanks,

Nikolas

Answer 1

[Star Strider]

For the first part, see if this does what you want:

M = randi([-5 5], 10, 5);                               % Create Data
[R,C] = find(M > 0);                                    % Positive Numbers
[Cu,ia] = unique(C);                                    % First Instance In ‘ia’
FirstPos = [Cu R(ia)]                                   % [Column Row] Meeting Criteria

Then you can subtract those numbers from whatever number you choose.

If you want the rows and columns to be linear indices instead (this can be easier to work with), use the sub2ind function to do the conversion from the ‘FirstPos’ array.

EDIT — Corrected typographical errors.