How to cut a matrix in Matlab?

Question

I would like to transform the matrix A into the matrix B without using cells (e.g. mat2cell) in Matlab, where

A=[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];

B=[1 2 3 10 11 12 19 20 21;
   4 5 6 13 14 15 22 23 24; 
   7 8 9 16 17 18 25 26 27];

Are these the exact dimensions, or can they change? Basically what you want to do is combine rows whose indices change in jumps of 3...? — Dev-iL, Nov 27 '14 at 12:03
[This](http://stackoverflow.com/questions/20336288/for-loop-to-split-matrix-to-equal-sized-sub-matrices) may help — Luis Mendo, Nov 27 '14 at 12:08

score 2 · Accepted Answer · answered Nov 27 '14 at 12:15

2

All you need is some reshape + permute magic -

N = 3;  %// Cut after every N rows and this looks like the no. of columns in A
B = reshape(permute(reshape(A,N,size(A,1)/N,[]),[1 3 2]),N,[])

answered Nov 27 '14 at 12:15

Divakar

218,885
19
262
358

score 0 · Answer 2 · answered Nov 27 '14 at 12:10

This builds a linear index to rearrange the entries of A and then reshapes into the desired matrix B:

m = 3; %// cut size in rows of A. Assumed to divide size(A,1)
n = size(A,2);
p = size(A,1);
ind = bsxfun(@plus, ...
      bsxfun(@plus, (1:m).', (0:n-1)*p), permute((0:p/m-1)*m, [1 3 2]));
B = reshape(A(ind(:)), m, [])

How to cut a matrix in Matlab?

2 Answers2