Duplicating rows in a matrix

Hi there

I have a matrix that i need to make twice as long. i.e i need to double the length of columns. eg i need:

[0 1 0 0]
[0 2 0 0]

to become:

[0 1 0 0]
[0 1 0 0]
[0 2 0 0]
[0 2 0 0]

Thanks

[Stephen23]

Just use REPELEM: https://www.mathworks.com/help/matlab/ref/repelem.html

A = [0,1,0,0;0,2,0,0]

A = 2×4

0 1 0 0 0 2 0 0

B = repelem(A,2,1)

B = 4×4

0 1 0 0 0 1 0 0 0 2 0 0 0 2 0 0

Answer 1

[Star Strider]

Try this:

M = [0 1 0 0
     0 2 0 0];

M2 = repmat(M, 1, 2);
M2 = reshape(M2', [], 4)'

producing:

M2 =
     0     1     0     0
     0     1     0     0
     0     2     0     0
     0     2     0     0

You could combine both calculations into a one-line calcualtion if you want to.

EDIT —

Generally, for ‘N’ repitions, the code becomes:

N = 4;                                  % Number Of Repititions
Mn = repmat(M, 1, N)
Mn = reshape(Mn', [], 2*N)'
producing: 
Mn =
     0     1     0     0
     0     1     0     0
     0     1     0     0
     0     1     0     0
     0     2     0     0
     0     2     0     0
     0     2     0     0
     0     2     0     0

[Matthew Allison]

elegant solution.

to make this a truly generic solution, the 2*N should be replaced by m*N, where m is the number of rows being duplicated. The 2 assumes that the original array has only 2 rows.

[Stephen23]

@Matthew Allison if you think that is elegant, just wait until you see REPELEM in action:

M = [0,1,0,0;0,2,0,0]

M = 2×4

0 1 0 0 0 2 0 0

Mn = repelem(M,2,1)

Mn = 4×4

0 1 0 0 0 1 0 0 0 2 0 0 0 2 0 0

REPELEM was introduced in R2015a, it is not clear why StarStrider avoided using it here.

[Star Strider]

@Matthew Allison — Thank you!

@Stephen — Because I wanted to make it general enough to work with earlier versions as well.