Copy a row or column of a matrix and insert it in the next row/column

Question

I was wondering if there is an easy way in MATLAB to do the following operation: I'd like to copy a row or column of a matrix and insert it in the next row/column.

For example: given a 3x3 matrix

1 2 3
4 5 6
7 8 9

I'd like to copy the first row and insert it as a second row:

1 2 3
1 2 3
4 5 6
7 8 9

Can someone advise how I could accomplish this in MATLAB? Thanks!

Answer 1

You can simply repeat the indices of the rows you'd like to repeat

A = A([1 1 2 3],:)

Answer 2

To insert row number source as row number target:

A = [A(1:target-1,:); A(source,:); A(target:end,:)];

Answer 3

A = [A(1,:); A];

Answer 4

I know this is a really old topic, but this post was coming up in searches I did for the same problem when I was looking for a specific Matlab function I couldn't remember the name of--padarray.

So, you could do:

A = [1 2 3; 4 5 6; 7 8 9];

A = padarray(A,[1 0],'replicate','pre');

This is often helpful if, for example, A is the output of a function that you have not saved explicitly, so you don't know what the first row is. Anyhow, hope this helps someone!