Reducing the computation time using a for loop

2 views (last 30 days)
A is a matrix with a bigger size than the B matrix. B is a subset of A (except the last column that I am trying to fill A;s last column with the respective values of B's last column). I wrote the following loop that has been running for more than an hour although it should be simple. I hoe someone can help me to reduce the computation time:
for m=1:size(A,1)
for n=1:size(B,1)
x0a=A(:,2)==B(n,2) & A(:,1)==B(n,1);
if ~isempty(x0a)
A(m,end)=B(x0a,end);
end
end
end

Accepted Answer

Guillaume
Guillaume on 11 Oct 2016
Edited: Guillaume on 11 Oct 2016
You do not need a loop at all if you use ismember:
[isinB, Brow] = ismember(A(:, [1 2]), B(:, [1 2]), 'rows');
A(isinB, end) = B(Brow(isinB), end);
edit: silly typo
  2 Comments
Danielle Leblance
Danielle Leblance on 11 Oct 2016
I am receiving an error Index exceeds matrix dimensions.
Error in AvgA (line 7) [isinB, Brow] = ismember(A(:, [1 2]), B(:, [1 2], 'rows'));
Guillaume
Guillaume on 11 Oct 2016
You corrected my typo, but not correctly. The missing closing bracket was supposed to go at the end of B(:, [1 2]).
I've now fixed it in my answer.

Sign in to comment.

More Answers (0)

Categories

Find more on MATLAB in Help Center and File Exchange

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!