Copy every nth column of a numpy array

Question

How would you copy the first element and every element of the nth column in another array?

For example, supposed you have the array below:

array{[1,2,3,4,5],
      [1,2,3,4,5],
      [1,2,3,4,5]}

I want to choose the first element and every 2nd element so I would have:

array{[1,3,5],
      [1,3,5],
      [1,3,5]}

Answer 1

You can use slicing against the columns

>>> a
array([[1, 2, 3, 4, 5],
       [1, 2, 3, 4, 5],
       [1, 2, 3, 4, 5]])

>>> a[:, ::2]
array([[1, 3, 5],
       [1, 3, 5],
       [1, 3, 5]])

As mentioned by @tobias_k if you want to make an actual copy of this sliced array, you can use numpy.copy to make sure modifications don't affect the original array

>>> np.copy(a[:, ::2])
array([[1, 3, 5],
       [1, 3, 5],
       [1, 3, 5]])