Shuffling non-zero elements of each column in a matrix

Question

Antonio 2018-4-13

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https://ww2.mathworks.cn/matlabcentral/answers/394776-shuffling-non-zero-elements-of-each-column-in-a-matrix

评论： Antonio 2018-4-13

I want to shuffle non-zero elements of each column in a matrix but keep the zero elements at the same place. Like I have this:

A = 
 [10    0     30    40    50    60
  0     31    41    0     61
   22    32    42    0     62
  23    0     43    0     63
   24    34    44    54    64
  0     35    0     0     65
  26    36    46    56    66]

And I want this:

B =
   [13    0     32    44    54    64
  0     35    42    0     63
   24    36    40    0     61
  23    0     43    0     62
   22    31    41    56    60
  0     30    0     0     66
  26    34    46    50    65]

So herein I have the zeros at the exact same place (i.e. ~A = ~B) and the non-zero elements are shuffled. Obviously shuffling the columns using 'randperm' does not work as it does not allow me to keep zeroes at the same place!

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Answer 1

James Tursa 2018-4-13

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https://ww2.mathworks.cn/matlabcentral/answers/394776-shuffling-non-zero-elements-of-each-column-in-a-matrix#answer_315016

编辑：James Tursa 2018-4-13

在 MATLAB Online 中打开

You're probably going to need a loop for this since the number of non-zero elements in a column is not constant across all the columns. For each column, use randperm on the non-zero elements. E.g., the process for one column:

A = your matrix
Ac = A(:,1); % a column
z = Ac ~= 0; % the non-zero element logical indexes
Az = Ac(z); % the non-zero elements
A(z,1) = Az(randperm(numel(Az))); % the shuffled elements replaced

Or, if you want a new matrix B as a result then copy A into B first and operate on B.

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James Tursa 2018-4-13

Put everything in the loop, not just the last two lines. Change the 1 to your loop index variable.

Antonio 2018-4-13

@James Tursa Oh man .. since you didn't put it in a loop yourself I thought it is way more complicated than that lmao. Thanks a bunch anyway it works perfect!

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