How do I compare to matrices with each other?

Hi Everyone,

I have two different matrices with diffrent sizes. for example one of them is 1000*3 and the other one is 5000*3.

How can I select/compare the line (I mean 1000 rows of these 5000 rows will be the same in these two matrices) and keep it in another matrice?

box1=cut2d(:,2:4);

box2=rombohedral(:,1:3);

if box1==box2

rombohedral2d=rombohedral;

end

The if part is not working.

[Ridwan Alam]

So ... box1 is 1000x3 and box2 is 5000x3?

When you said "1000 rows of these 5000 rows will be the same in these two matrices", did you mean "consecutive" rows?

[Hamed Nobarani]

Yes for the first question and I will hive you an example for second one:

Box 1 : 1 2 3

4 5 6

Box 2 : . . .

1 2 3

. . .

4 5 6

So now I want to just keep the rows of box 2 which it has the same number in three columns in box 1. Because in box 2 I have more information and I want just too keep some of them.

Answer 1

[Ridwan Alam]

box1=cut2d(:,2:4);
box2=rombohedral(:,1:3);

[index1,index2] = ismember(box1,box2,'rows');
% index2 holds the indices of the rows that are also in box1

rombohedral2d=rombohedral(index2,:); % I assume you want all the columns, not only 3, right?
% if you want only those 3 columns, use:
% rombohedral2d=rombohedral(index2,1:3);

[Hamed Nobarani]

Exactly.

Thanks.

Answer 2

[Erivelton Gualter]

If I understood right, you want to compare the first 1000 rows of these two matrix.

% Sample Matrix
A = rand(1000, 3);
B = rand(5000, 3);

% C contains 0 and 1 as a results of comparing A and B. Since A and B were rand created, 
% matrix C will probably contains only zeros (1000x3)
C = A == B(1:1000,:)

% As a example, lets chage the first rows for each matrix:
A(1,:) = [0 1 2];
B(1,:) = [0 1 5]
C = A == B(1:1000,:)

% The result will be 
% C = [1 1 0;
%      0 0 0 .....

It may be not what you want, but can give you some insigth.

[Hamed Nobarani]

Actually, it is not just the first 1000 rows I want to check all of the rows of the second box.