How to get the number of columns in a matrix?

Question

Suppose I specify a matrix A like

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

how can I query A (without using length(A)) to find out it has 3 columns?

Answer 1

Use the size() function.

>> size(A,2)  Ans =     3 

The second argument specifies the dimension of which number of elements are required which will be '2' if you want the number of columns.

Official documentation.

Answer 2

While size(A,2) is correct, I find it's much more readable to first define

rows = @(x) size(x,1);  cols = @(x) size(x,2); 

and then use, for example, like this:

howManyColumns_in_A = cols(A) howManyRows_in_A    = rows(A) 

It might appear as a small saving, but size(.., 1) and size(.., 2) must be some of the most commonly used functions, and they are not optimally readable as-is.