Remove a column from a matrix in GNU Octave

Question

In GNU Octave, I want to be able to remove specific columns from a matrix. In the interest of generality. I also want to be able to remove specific rows from a matrix.

Suppose I have this:

mymatrix = eye(5)  mymatrix =  Diagonal Matrix     1   0   0   0   0    0   1   0   0   0    0   0   1   0   0    0   0   0   1   0    0   0   0   0   1 

I want to remove columns 2 and 4, but when I remove column 2, the position of column 4 has moved to column 3, and that makes my head hurt. There has to be a better way!

Answer 1

In case you don't know the exact number of columns or rows you can use the magic "end" index, e.g.:

mymatrix(:,2:end)  % all but first column  mymatrix(2:end,:)  % all but first row 

This also allows you to slice rows or columns out of a matrix without having to reassign it to a new variable.