How to compare elements of a 2D array with other elements of the same array.

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Sahil Islam
Sahil Islam 2022-3-8
回答： Arif Hoq 2022-3-8
I have an 2D array where I have to compare each element with all the others and save the index position if the two elements are equal.
How can I do that using lesser for loops?
I can't give the code for array here because it is a big data. Can you answer with an example.
Thanks .
Edit: Initial question might be unclear.
Just to give an example, suppose I have an array A:
A=[1 2 3 ; 2 9 5; 4 1 8]
Here A(1,1) and A(3,2) are both =1
I need to detect all of such pairs or collection of index(if more than two).

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回答（2 个）

KSSV
KSSV 2022-3-8
You can use ismember. Read about the function ismember.
Arif Hoq
Arif Hoq 2022-3-8
Ran in:
A=[1 2 3 ; 2 9 5; 4 1 8]
A = 3×3
1 2 3 2 9 5 4 1 8
[A1 C]=ismember(A(:),A);
A2=sort(C); % sorting index
A3=A(A2) % value of A those are identical
A3 = 9×1
1 1 2 2 4 9 3 5 8

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