combinations with 2 columns

Asked by sampath kumar punna on 18 Oct 2019

Latest activity Answered by Jos (10584) on 21 Oct 2019

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Hi guys can you help out in creating a combination

if we got 2 columns and 3 rows

1 2

Combination 1: 1,1,1

Combination 2: 1,1,2

Combination 3: 1,2,1

Combination 4:2,1,1

Combination 6: 2,2,2

Combination 7: 2,2,1

Combination 8: 2,1,2

Combination 9: 1,2,2

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Answer by Athul Prakash on 21 Oct 2019

Hi Sampath,

Look like you want to select exactly 1 element per row, from among all columns of the matrix. Hence, if there are m rows and n elements per row (or n columns), there would be n^m combinations generated (2^3 = 8 in your question).

Solution using combvec()

Please read up on combvec here:

https://www.mathworks.com/help/deeplearning/ref/combvec.html

If we give row vectors as inputs to combvec(), it generates all possible combinations of elements from those row vectors. Hence, we may pass each row to combvec() as a separate argument, as illustrated below:

mat = [1 2; 1 2; 1 2];
ans = combvec(mat(1,:), mat(2,:), mat(3,:))   % Each column of 'ans' is one of your desired combinations

If the number of rows is not known, you may want to use a for loop:

% suppose 'mat' contains the data
num_rows = size(mat,1);
combs = mat(1,:);
for i=2:num_rows
    combs = combvec(mat(i,:), combs);
end
disp(combs);

Hope it Helps!

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Answer by Andrei Bobrov on 21 Oct 2019

Combination = fullfact([2 2 2]);

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Answer by Jos (10584) on 21 Oct 2019

Take a look at ALLCOMB on the File Exchange:

https://uk.mathworks.com/matlabcentral/fileexchange/10064-allcomb-varargin

X = [1 2 ; 3 4 ; 5 6] ; % input matrix
[n, m] = size(X) % [n m]
C = mat2cell(X, ones(1,n), m) 
B = allcomb(C{:}) 

You are now following this question

sampath kumar punna (view profile)