Indices of 'convolution' aka finding indicies of one matrix from a set of matrices in another matrix

Hi

I'm wondering if there is an efficient way to do the following.

Set up:

A=randi(2,10,3); B=(A(:,1)==1); C=A(B); indsOfC=myfun(C);

So C is a matrix whose rows are just those where A had a first column of 1, and inds is the result of doing some function with C as its argument. What I'm wondering is if there is an easy way of relating the indicies of C to the indices of A.

Thanks

[Sean de Wolski]

Could you show a small example with input/ops/expected output please.

Answer 1

[Fangjun Jiang]

Not very clear what you are asking. Using your example, if you run [I,J,V]=find(B), is the matrix I what you are looking for?

[Brendan]

It is, thank you. Didn't think of that for some reason.