FInd vector in matrix

Lets assume that I have a matrix A 300x2 with x y coordinates. I want to find how many times a specific [x y] exists in this matrix A. I ve tried this but find can search only single values.

i = find(A == [x y]);

Any idea?????

[Azzi Abdelmalek]

[Kris zenitis commented]

Yeah thank you man!!

Answer 1

[Jan]

Another method:

I = sum(A(:, 1) == x & A(:, 2) == y);

EDITED: Buggy multiplication method removed. Thanks Andrei!

This method is about 50 times faster than ISMEMBER(A, b, 'rows').

[Andrei Bobrov]

Hi Jan! may be it?

I = sum((A(:, 1) == x).* (A(:, 2) ==y));

[Jan]

@Andrei: You are right. But the multiplication is slower than the AND operator. Therefore I've removed this method.

[Esubalew]

Hi Jan,

The method you suggested above is a good one, but incase if A is 1000 by 100 matrix or a bigger matrix, it there a better way to cind the row of A, A_i such that A_i ==v for some vector v of size =size(A,2)?

Thank you!

Answer 2

[Matt Fig]

For example:

A = reshape(1:12,6,2) % A sample matrix for demonstration...
I = ismember(A,[4 10],'rows');

If you want to find how many there are, use:

S = sum(I)