# Find the common elements in same indices in two arrays.

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Md. Asadujjaman on 6 Apr 2022
Commented: Voss on 6 Apr 2022
Suppose,
A = [1001 1002 1003 2001 2002 1004 1005 2003 2004 2005]
B = [1001 1002 2001 2002 1003 1004 2003 1005 2004 2005]
X and Y are two arrays with zero elements
X = [0 0 0 0 0 0 0 0 0 0]
Y = [0 0 0 0 0 0 0 0 0 0]
(1) Now I want to find the common elements that are in the same indices of A and B and put in X and Y.
X = [1001 1002 0 0 0 0 1004 0 2004 2005]
Y = [1001 1002 0 0 0 0 1004 0 2004 2005]
(2) Now generate two random indices; e.g., 5 and 7
Now, I want to replace the elements of X and Y between the random indices (5 and 7) with the elements of A and B, respectively.
X = [1001 1002 0 0 2002 1004 1005 0 2004 2005]
Y = [1001 1002 0 0 1003 1004 2003 0 2004 2005]
(3) Now I want to replace the zero elements of X with the elements of B (that are not in X; i.e., 2001, 1003 and 2003), following the same relative order of the elements.
Also, I want to replace the zero elements of Y with the elements of A (that are not in Y; i.e., 2001, 2002 and 1005), following the same relative order of the elements.
X = [1001 1002 2001 1003 2002 1004 1005 2003 2004 2005]
Y = [1001 1002 2001 2002 1003 1004 2003 1005 2004 2005]
How can I do these? Thanks in advance.
Voss on 6 Apr 2022
You can use randi to generate random indices, e.g.:
% generate two integers between 1 and numel(X) - the number of elements of
% X - and sort them so that rand_idx(2) >= rand_idx(1) so you can do
% indexing like: X(rand_idx(1):rand_idx(2))
rand_idx = sort(randi(numel(X),1,2));

Davide Masiello on 6 Apr 2022
clear,clc
A = [1001 1002 1003 2001 2002 1004 1005 2003 2004 2005];
B = [1001 1002 2001 2002 1003 1004 2003 1005 2004 2005];
X = zeros(size(A));
X(A == B) = A(A == B);
Y = X;
rand_idx = [5,7];
X(rand_idx) = A(rand_idx);
Y(rand_idx) = B(rand_idx);
X(X == 0) = B(X == 0);
Y(Y == 0) = A(Y == 0);
fprintf(['X = [',repmat('%d ',size(X)),']'],X)
X = [1001 1002 2001 2002 2002 1004 1005 1005 2004 2005 ]
fprintf(['Y = [',repmat('%d ',size(Y)),']'],Y)
Y = [1001 1002 1003 2001 1003 1004 2003 2003 2004 2005 ]