Error when using find function

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Chau Chin Haw
Chau Chin Haw 2021-1-1
评论： Stephen23 2021-1-2
There are 2 matrix, A and B
A=[1
2]
B=[1
2
2]
% Check if the element in A is repeated at B
Check = find (B(:,1)==A)
%Error
%Unable to perform assignment because the left and right sides have a different number of elements.
Check = find (B(1:2,1)==A) %working fine
I need the value 2 in A to be compared with both value 2 in B. I was only manage to compre 2 element with 2 element. Is there any methos to achieve comparing array with 2 element with array with 3 element by using "find" fucntion? Thanks in advance.

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回答（2 个）

Paul
Paul 2021-1-1
Maybe you want to start with ismember?
doc ismember
Walter Roberson
Walter Roberson 2021-1-1
%Unable to perform assignment because the left and right sides have a different number of elements.
That would give
Matrix dimensions must agree.
I need the value 2 in A to be compared with both value 2 in B.
find(B == A(2))
Is there any methos to achieve comparing array with 2 element with array with 3 element by using "find" fucntion?
>> [R,C] = find(B == A.')
R =
1
2
3
C =
1
2
2
Read that as B(1) = A(1), B(2) = A(2), B(3) = A(2)
But I have to wonder whether you really want to use find. I can't tell what you are really aiming to do with the information. I suggest you consider
>> [wasthere, idx] = ismember(B,A)
wasthere =
3×1 logical array
1
1
1
idx =
1
2
2
Or perhaps ismember(A,B) depending what you are trying to do.
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Paul
Paul 2021-1-2
As has been stated in two different answers, the function ISMEMBER is what you need. Have you looked at its documentation? If so and its not satisfactory, why not?
Stephen23
Stephen23 2021-1-2
This is a very odd definition of comparing two vectors: "A(1) compared with B(1), A(2) compared with B(2), A(2) once again compared with third element of B". In any case, neither find nor ismember will do that unusual comparison, you will have to DIY.

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