Repmat the rows of a matrix

Dear;

I would like to efficiently repmat the rows of a matrix to for a new one; For example the matrix:

A=[2 0 0;
   0 2 0;
   0 0 2;
  ];

I want to replicate 3 times the rows to form the following matrix:

B=[2 0 0;
   2 0 0;
   2 0 0;
   0 2 0;
   0 2 0;
   0 2 0;
   0 0 2;
   0 0 2;
   0 0 2;
  ];

Is there any vectorized way to perform this operation (without using for loops).

Thanks in advance;

Answer 1

[Jordan Lui]

Be careful with the other answer. It will not work for more general cases. Instead, try this:

numRep = 3;
[r,c] = size(A);
B1 = repmat(A', numRep , 1);
B = reshape(B1, [], r * numRep)';

Answer 2

[Star Strider]

This works:

A=[2 0 0;
   0 2 0;
   0 0 2];

[Ar,Ac] = size(A);
B1 = repmat(A, Ar, 1);
B = reshape(B1, [], size(B1,1))'

B =
     2     0     0
     2     0     0
     2     0     0
     0     2     0
     0     2     0
     0     2     0
     0     0     2
     0     0     2
     0     0     2

[Jordan Lui]

This solution does not work on an example like this:

  A=[2 7 8;
   4 2 8;
   5 6 2
   -1 -1 -1;
    ];

Using a non square matrix and filling the off diagonals shows the issue. Result will be:

B =

     2     4     5
    -1     2     4
     5    -1     2
     4     5    -1
     2     4     5
    -1     7     2
     6    -1     7
     2     6    -1
     7     2     6
    -1     7     2
     6    -1     8
     8     2    -1
     8     8     2
    -1     8     8
     2    -1     8
     8     2    -1

The following solution works:

numRep = 3;
[r,c] = size(A);
B1 = repmat(A', numRep , 1);
B = reshape(B1, [], r * numRep)';