MATLAB: How to rearrange data in matrix rows

rearrangereshaperowwise

Hi,
I have a large matrix (14484×10) on this form:
[20031119 1 2 3 4 5 6 7 8 9;
10 11 12 13 14 15 16 17 18 19;
20 21 22 23 24 25 26 27 28 29;
30 31 NaN NaN NaN NaN NaN NaN NaN NaN;
20031120 1 2 3 4 5 6 7 8 9;
10 11 12 13 14 15 16 17 18 19;
20 21 22 23 24 25 26 27 28 29;
30 31 NaN NaN NaN NaN NaN NaN NaN NaN;
20031121 1 2 3 4 5 6 7 8 9;
...and so on]
I want to rearrange the rows so that the first 4 rows turn makes the first row in the new matrix, the next 4 rows makes the second row etc, so that the resulting matrix looks like this:
[20031119 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31;
20031120 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31;
...and so on]
(I don't need the NaNs, but it's of course OK to keep them and delete them later.)
How do I do this? I have tried to do it using reshape, but it seems to me that reshape works columnwise and not rowwise.
I would appreciate any help!

Best Answer

reshape, like pretty much all MATLAB operations, works columnwise. So you just need to transpose, reshape, transpose:
X = [20031119 1 2 3 4 5 6 7 8 9;
10 11 12 13 14 15 16 17 18 19;
20 21 22 23 24 25 26 27 28 29;
30 31 NaN NaN NaN NaN NaN NaN NaN NaN;
20031120 1 2 3 4 5 6 7 8 9;
10 11 12 13 14 15 16 17 18 19;
20 21 22 23 24 25 26 27 28 29;
30 31 NaN NaN NaN NaN NaN NaN NaN NaN];
out = reshape(X.',[],size(X,1)/4).';
creates this output matrix:
>> out
out =
 Columns 1 through 9:
   20031119          1          2          3          4          5          6          7          8
   20031120          1          2          3          4          5          6          7          8
 Columns 10 through 18:
          9         10         11         12         13         14         15         16         17
          9         10         11         12         13         14         15         16         17
 Columns 19 through 27:
         18         19         20         21         22         23         24         25         26
         18         19         20         21         22         23         24         25         26
 Columns 28 through 36:
         27         28         29         30         31        NaN        NaN        NaN        NaN
         27         28         29         30         31        NaN        NaN        NaN        NaN
 Columns 37 through 40:
        NaN        NaN        NaN        NaN
        NaN        NaN        NaN        NaN
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