Repmat the rows of a matrix
3 views (last 30 days)
Show older comments
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;
0 Comments
Answers (2)
Jordan Lui
on 2 Dec 2020
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)';
0 Comments
Star Strider
on 20 Jan 2016
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
1 Comment
Jordan Lui
on 2 Dec 2020
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)';
See Also
Categories
Find more on Logical in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!