Matlab: column of empty matrix

Question

Wondering if anyone could help me with this.

For getting the first column x of a matrix A. I use x = A(:,1). Every so often, the matrix A is empty, in which case I would like my column to also be empty. But with Matlab, the code exits with error “Index exceeds matrix dimensions”. Is there a way to prevent it from exiting, and instead give me []?

(I could of course write an “if” statement using isempty(A), but that’s annoying since my code is filled with dozens of places where I may have empty matrices.)

Answer 1

You can use logical indexing:

A(:,end>0);

For non-empty matrices it will be

A(:,logical(1));

which returns the first column, and for empty matrices it will be

A(:,logical(0));

which returns an empty column matrix.

Answer 2

This is kinda clumsy, but it works and is shorter than an if or try:

A(:,1:min(1,size(A,2)))

or

A(:,1:9999999999:size(A,2))