How to get the combinations of elements of two arrays?
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Hi! I need to generate the combinations of elements of two arrays with different lengths. For example, if
A = [1,2,3]; B = [4,5];
I wish to get all combinations of elements from two arrays as
C = [1 4;1 5;2 4;2 5;3 4;3 5];
What comes to my mind is
[m,n] = meshgrid(A,B');
[C(:,1),C(:,2)] = deal(reshape(m,[],1),reshape(n,[],1));
Is there any more straight way to accomplish this?
And further, if I have three or more arrays to combine, what should I do?
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Accepted Answer
Stephen23
on 3 Dec 2018
Edited: Stephen23
on 27 Oct 2023
A = [1,2,3];
B = [4,5];
[n,m] = ndgrid(B,A);
out = [m(:),n(:)]
"And further, if I have three or more arrays to combine, what should I do?"
Put them all in a cell array and use two comma-separated lists:
C = {A,B};
[C{end:-1:1}] = ndgrid(C{end:-1:1});
EDIT: using CAT & RESHAPE is probably the most efficient approach:
n = numel(C);
E = reshape(cat(n,C{:}),[],n)
This approach is from Dyuman Joshi's comment here:
4 Comments
Stephen23
on 26 Oct 2023
@Dyuman Joshi: thank you, that is a very good approach! I copied it into my answer so that it does not get lost in the comments.
Dyuman Joshi
on 26 Oct 2023
You are welcome!
Note that the usage of the indices in reverse order is to obtain the output in lexicographical manner (in the order of the values provided in the inputs).
More Answers (3)
Jeff Miller
on 3 Dec 2018
For example:
>> A = [1,2,3]; B = [4,5];
>> C=allcomb(A,B)
C =
1 4
1 5
2 4
2 5
3 4
3 5
Mike Croucher
on 4 Apr 2023
Edited: Mike Croucher
on 4 Apr 2023
As of MATLAB R2023a, the new combinations function can do this for you. Details at The new combinations function in MATLAB – for cartesian products and parameter sweeps » The MATLAB Blog - MATLAB & Simulink (mathworks.com)
>> A = [1,2,3];B=[4,5];
>> C = combinations(A,B)
C =
6×2 table
A B
_ _
1 4
1 5
2 4
2 5
3 4
3 5
The result is a table. When all data types are compatible (as is the case here) you can get the matrix like this
>> C.Variables
ans =
1 4
1 5
2 4
2 5
3 4
3 5
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ROHIT KHATRI
on 26 Oct 2023
In MATLAB R2017b allcomb and combinations codes not working. So please tell me what can i do?
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