2 个投票

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?????

请先登录，再回答此问题。

 采纳的回答

Jan
Jan 2011-5-14

7 个投票

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').

3 个评论
显示 1更早的评论 隐藏 1更早的评论

Andrei Bobrov
Andrei Bobrov 2011-5-14
Hi Jan! may be it?
I = sum((A(:, 1) == x).* (A(:, 2) ==y));
Jan
Jan 2011-5-14
@Andrei: You are right. But the multiplication is slower than the AND operator. Therefore I've removed this method.
Esubalew
Esubalew 2017-7-25
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!

请先登录，再进行评论。

更多回答（1 个）

Matt Fig
Matt Fig 2011-5-14

1 个投票

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)

类别

在 帮助中心 和 File Exchange 中查找有关 Matrices and Arrays 的更多信息

标签

Community Treasure Hunt

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

Start Hunting!

Translated by