Sorting matrices in matlab

Question

Matija Kosak 2018-7-5

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/408961-sorting-matrices-in-matlab

评论： Matija Kosak 2018-7-5

采纳的回答： Stephen23

在 MATLAB Online 中打开

Hello,

I have a NxM matrix:

Random A for example 10x5

A =

   8     7     1     4
   8     8     1     7
   8     2     8     8
   3     2    10     6
   7     6     7     8
   6     5     2     3
   4     9     8     8
   1     8     2    10
   8     8     2     9
   4     1     7     1

I would like to make another matrix (B) that contains first every N, N+2, N+4...and after them N+1,N+3.. ect

B =

   8     7     1     4
   8     2     8     8
   7     6     7     8
   4     9     8     8
   8     8     2     9
   8     8     1     7
   3     2    10     6
   6     5     2     3
   1     8     2    10
   4     1     7     1

Thank you.

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Stephen23 2018-7-5

Note that this is a topic of indexing/rearranging the elements, where the element values are not relevant to the new order (only their indices are). Sorting depends only on the element values (not their indices).

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Answer 1

Stephen23 2018-7-5

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https://ww2.mathworks.cn/matlabcentral/answers/408961-sorting-matrices-in-matlab#answer_327609

在 MATLAB Online 中打开

>> B = A([1:2:end,2:2:end],:)
B =
  8    7    1    4
  8    2    8    8
  7    6    7    8
  4    9    8    8
  8    8    2    9
  8    8    1    7
  3    2   10    6
  6    5    2    3
  1    8    2   10
  4    1    7    1

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Stephen23 2018-7-5

编辑：Stephen23 2018-7-5

在 MATLAB Online 中打开

@Matija Kosak: I would use reshape and permute to generalize this (note that the number of rows N has to be exactly divisible by R):

>> A = randi(99,12,5) % size NxM
A =
 89   14   49   65
 33   18   98   14
 59   53   29   54
 69   51   27   50
 96   86   17   55
 14   56   30   54
 16   17   43   60
 73   78   80    3
 31   23   84   54
 17   26   72   29
 54   55   46    2
 67    1   99   29
>> R = 4; % N must be divisible by R.
>> S = size(A);
>> B = reshape(permute(reshape(A,R,[],S(2)),[2,1,3]),S)
B =
 89   14   49   65
 96   86   17   55
 31   23   84   54
 33   18   98   14
 14   56   30   54
 17   26   72   29
 59   53   29   54
 16   17   43   60
 54   55   46    2
 69   51   27   50
 73   78   80    3
 67    1   99   29
>> C = A([1:4:end,2:4:end,3:4:end,4:4:end],:) % needs to match this!
C =
 89   14   49   65
 96   86   17   55
 31   23   84   54
 33   18   98   14
 14   56   30   54
 17   26   72   29
 59   53   29   54
 16   17   43   60
 54   55   46    2
 69   51   27   50
 73   78   80    3
 67    1   99   29
>> isequal(B,C)
ans = 1