How To Iterate Over Columns Of A Matrix?

In python if a define: a = arange(9).reshape(3,3) as a 3x3 matrix and iterate: for i in a: It'll iterate over the matrix's rows. Is there any way to iterate over columns?

Solution 1:

How about

for i in a.transpose():

or, shorter:

for i in a.T:

This may look expensive but is in fact very cheap (it returns a view onto the same data, but with the shape and stride attributes permuted).

Solution 2:

Assuming that a is a well formed matrix, you could try something like:

b = zip(*a)
for index in b:
   ...