How can I do setdiff() between 2 arrays row by row without a loop?

Question

Izan Segarra 2019-2-21

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/446257-how-can-i-do-setdiff-between-2-arrays-row-by-row-without-a-loop

评论： Izan Segarra 2019-2-21

I'm trying to do the difference between 2 arrays with setdiff function but I don't get the expected result.

    
A = [15  8  5  9  10  14  17  7  20  12  6  16  2  4  11  13  3  1  19  18
19 13 15   1  16   6 14  17   8 11  18 20  5   2  12  7  9   4   3
8  5  9  10  14  17  7  20  12  6  16  2  4  11  13  3  1  19  18
12  3 14   4  19   2 16  10  18 20   6 15  5   7  17  1  9  11   8
12  3 14   4  19   2 16  10  18 20   6 15  5   7  17  1  9  11   8];
 
B = [16    19    15     5     8     1     3    20    14    18
  14    13     2    20     9    15     7     6    12
   2    12    13     4     8     5    19    18    20
  10    19    13    15     1    16     6    14    17
  11     6    10    13     7    16    19    15     5];

When I execute the instruction I get:

setdiff(A,B)
ans =
  0×1 empty double column vector
  

But I would like to get:

  out =[ 9    10    17     7    12     6     2     4    11    13
        10    19     1    16    17     8    11    18     5     3
        15     9    10    17     7     6    16    11     3     1
        12     4     2    18    20     5     7     9    11     8
         3    14     4     2    18    20    17     1     9     8];
     

Is there some way to get it without a loop?

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Answer 1

Fangjun Jiang 2019-2-21

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https://ww2.mathworks.cn/matlabcentral/answers/446257-how-can-i-do-setdiff-between-2-arrays-row-by-row-without-a-loop#answer_362110

在 MATLAB Online 中打开

While your result shows that out is a 5x10 array, it is not guaranted in a generic case, because if you do setdiff() row by row on A and B, the number of elements will not always be the same row by row.

Why so obsessed with "no for-loop"? For-loop could be simple, faster and easy to understand. I can think of one way to do your task without for-loop, but do you think it is easy to follow?

ca=mat2cell(A,repmat(1,1,size(A,1)),size(A,2))
cb=mat2cell(B,repmat(1,1,size(B,1)),size(B,2))
out=cell2mat(cellfun(@(a,b) setdiff(a,b),ca,cb,'uniformoutput',false))