Shuffle matrix rows so that common elements are in completely different order than in a said row

Question

Pseudoscientist 2019-4-26

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https://ww2.mathworks.cn/matlabcentral/answers/458726-shuffle-matrix-rows-so-that-common-elements-are-in-completely-different-order-than-in-a-said-row

编辑： Matt J 2019-4-26

采纳的回答： Matt J

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Say we have a matrix row 'current_row'

1 2 3

and a matrix A

1 2 5

1 3 6

2 4 3

The task is to re-arrange matrix A so that the common elements with 'current:_row' in each row are in compelely different indices.

One solution would be:

5 1 2

6 3 1

2 3 4

So that

for i=1:size(A,1)
    find(current_row == A(i,:))
end

gives always three []'s

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Matt J 2019-4-26

编辑：Matt J 2019-4-26

gives always three 0s

You mean gives []'s.

Pseudoscientist 2019-4-26

Oh yes true

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Answer 1

Matt J 2019-4-26

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https://ww2.mathworks.cn/matlabcentral/answers/458726-shuffle-matrix-rows-so-that-common-elements-are-in-completely-different-order-than-in-a-said-row#answer_372441

编辑：Matt J 2019-4-26

在 MATLAB Online 中打开

Here is a vectorized implementation of what John described.

[m,n]=size(A);
I=repmat((1:m).',1,n);
B=A; %copy for shuffling
pool=find(any(B==current_row,2));
while ~isempty(pool)
    
    p=numel(pool);
    
    [~,J]=sort(rand(p,n),2);
    
    B(pool,:)=B(  sub2ind([m,n], I(pool,:), J) );  %shuffle rows in 'pool'
    
    pool=find(any(B==current_row,2)); %narrow the search
    
end
result=Anew;

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Answer 2

John D'Errico 2019-4-26

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What you are looking for is a variation of derangement - thus a permutation such that no element is in the same location as it started.

A simple solution? Just continue to shuffle each other row until it meets the goal, that no common elements are in the same location as they are in current_row. Stop when it does, and then go on to the next row. WTP?

You can probably improve on that scheme a bit, by finding the elements in common between the two rows. Then first permute them into ANY locations, as long as they are not the same as the current_row. Having done that derangement operation, then permute the other elements into any random permutation.