I have a matrix
index in Matlab with size
GxN and a matrix
A with size
Let me provide an example before presenting my question.
clear N=3; G=2; M=5; index=[1 2 3; 13 14 15]; %GxN A=[1 2 3; 5 6 7; 21 22 23; 1 2 3; 13 14 15]; %MxN
I would like your help to construct a matrix
Response with size
Response(g,m)=1 if the row
A(m,:) is equal to
index(g,:) and zero otherwise.
Continuing the example above
Response= [1 0 0 1 0; 0 0 0 0 1]; %GxM
This code does what I want (taken from a previous question of mine - just to clarify: the current question is different)
Response=permute(any(all(bsxfun(@eq, reshape(index.', N, , G), permute(A, [2 3 4 1])), 1), 2), [3 4 1 2]);
However, the command is extremely slow for my real matrix sizes (
N=19, M=500, G=524288). I understand that I will not be able to get huge speed but anything that can improve on this is welcome.
Aproach 1: computing distances
If you have the Statistics Toolbox:
Response = ~(pdist2(index, A));
Response = ~(pdist2(index, A, 'hamming'));
This works because
pdist2 computes the distance between each pair of rows. Equal rows have distance
0. The logical negation
1 for those pairs of rows, and
Approach 2: reducing rows to unique integer labels
This approach is faster on my machine:
[~,~,u] = unique([index; A], 'rows'); Response = bsxfun(@eq, u(1:G), u(G+1:end).');
It works by reducing rows to unique integer labels (using the third output of
unique), and comparing the latter instead of the former.
For your size values this takes approximately 1 second on my computer:
clear N = 19; M = 500; G = 524288; index = randi(5,G,N); A = randi(5,M,N); tic [~,~,u] = unique([index; A], 'rows'); Response = bsxfun(@eq, u(1:G), u(G+1:end).'); toc
Elapsed time is 1.081043 seconds.