Permutation with repeating elements.

Question

Sourov Kumar Mondal 2022-10-16

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https://ww2.mathworks.cn/matlabcentral/answers/1827743-permutation-with-repeating-elements

编辑： Bruno Luong 2022-10-16

Hello, greetings! I have the following array, A= 1:7. I want to get all the possible permutations of seven elements and I am trying to get my answer like this

ans =

1 2 3 4 5 6 7

1 2 5 3 4 7 6

2 3 4 5 1 7 6...... etc

It should be easy. But in the 'A' matrix, 1 and 2 indicates the simillar thing; 3 and 4 indicates the simillar thing; 5, 6, and 7 indicates the simillar thing. So, in the 'ans' 1 2 3 4 5 6 7 and 2 1 4 3 7 6 5 will be same. I want the code to return the values without repitating it. Is there any way to do this?

note: I want this code to do linear indexing. So, I can't replace A with any other matrix. It has to be 1:7.

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Answer 1

Bruno Luong 2022-10-16

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https://ww2.mathworks.cn/matlabcentral/answers/1827743-permutation-with-repeating-elements#answer_1076373

在 MATLAB Online 中打开

Just brute force of filter out what is considered as duplicated

g = [1 1 2 2 3 3 3];
x = 1:7;
p = perms(x);
[~,i] = unique(perms(g),'rows');
p = p(i,:);
p
p = 210×7
     2     1     4     3     7     6     5
     2     1     4     7     3     6     5
     2     1     4     7     6     3     5
     2     1     4     7     6     5     3
     2     1     7     4     3     6     5
     2     1     7     4     6     3     5
     2     1     7     4     6     5     3
     2     1     7     6     4     3     5
     2     1     7     6     4     5     3
     2     1     7     6     5     4     3

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Sourov Kumar Mondal 2022-10-16

Thanks again for the answer!

Bruno Luong 2022-10-16

编辑：Bruno Luong 2022-10-16

在 MATLAB Online 中打开

Simplify lperms

function p = lperms(x, k)
p = nchoosek(x,k);
p = reshape(p(:,perms(1:k)),[],k);
end

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Answer 2

KSSV 2022-10-16

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https://ww2.mathworks.cn/matlabcentral/answers/1827743-permutation-with-repeating-elements#answer_1076278

在 MATLAB Online 中打开

 A = {[1 2], [3 4], [5 6 7]} ;
 iwant = perms(A)
iwant = 6×3 cell array
    {[5 6 7]}    {[  3 4]}    {[  1 2]}
    {[5 6 7]}    {[  1 2]}    {[  3 4]}
    {[  3 4]}    {[5 6 7]}    {[  1 2]}
    {[  3 4]}    {[  1 2]}    {[5 6 7]}
    {[  1 2]}    {[5 6 7]}    {[  3 4]}
    {[  1 2]}    {[  3 4]}    {[5 6 7]}

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Sourov Kumar Mondal 2022-10-16

Thanks for the answer. But this is keeping 1 and 2; 3 and 4; 5, 6, and 7 together always. The output I am looking for is just like normal permutations of 7 elements. but 1 and 2; 3 and 4; and 5,6 and 7 will behave like simillar elements. The no. of expected permutations would be (7! / (2! * 2! * 3!)). Is there any solution to this? thanks is advanced.

Sourov Kumar Mondal 2022-10-16