Sorting matrices in matlab

Hello,

I have a NxM matrix:

Random A for example 10x5

A =

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

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

Thank you.

[Stephen23]

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).

Answer 1

[Stephen23]

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

[Matija Kosak]

What if I have for example 14 rows between each other? Is there some loop or I have to write

B = A([1:14:end,2:14:end,3:14:end,4:14:end....14:14:end],:)

[Stephen23]

@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 =
   35   89   14   49   65
   76   33   18   98   14
   29   59   53   29   54
   63   69   51   27   50
   21   96   86   17   55
   60   14   56   30   54
   40   16   17   43   60
   62   73   78   80    3
   37   31   23   84   54
    8   17   26   72   29
   62   54   55   46    2
   31   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 =
   35   89   14   49   65
   21   96   86   17   55
   37   31   23   84   54
   76   33   18   98   14
   60   14   56   30   54
    8   17   26   72   29
   29   59   53   29   54
   40   16   17   43   60
   62   54   55   46    2
   63   69   51   27   50
   62   73   78   80    3
   31   67    1   99   29
>> C = A([1:4:end,2:4:end,3:4:end,4:4:end],:) % needs to match this!
C =
   35   89   14   49   65
   21   96   86   17   55
   37   31   23   84   54
   76   33   18   98   14
   60   14   56   30   54
    8   17   26   72   29
   29   59   53   29   54
   40   16   17   43   60
   62   54   55   46    2
   63   69   51   27   50
   62   73   78   80    3
   31   67    1   99   29
>> isequal(B,C)
ans = 1

[Matija Kosak]

That's not good for what I need because it mix numbers. I would need for numbers in rows to be same.

[Matija Kosak]

It works now, thank you a lot :)