Question

I have two matrices A and B, both contain a list of event start and stop times:

A(i,1) = onset time of event i
A(i,2) = offset time of event i
B(j,1) = onset of event j
...

My goal is to get two lists of indecies aIdx and bIdx such that A(aIdx,:) and B(bIdx,:) contain the sets of events that are overlapping.

I’ve been scratching my head all day trying to figure this one out. Is there a quick, easy, matlaby way to do this?

I can do it using for loops but this seems kind of hacky for matlab:

aIdx = [];
bIdx = []
for i=1:size(A,1)
    for j=i:size(B,1)
        if overlap(A(i,:), B(j,:)) % overlap is defined elsewhere
            aIdx(end+1) = i;
            bIdx(end+1) = j;
        end
    end
end

Answer 1

Here’s a zero loop solution:

overlap = @(x, y)y(:, 1) < x(:, 2) & y(:, 2) > x(:, 1)
[tmp1, tmp2] = meshgrid(1:size(A, 1), 1:size(B, 1));
M = reshape(overlap(A(tmp1, :), B(tmp2, :)), size(B, 1), [])';
[aIdx, bIdx] = find(M);