How to remove every other element of an array in python? (The inverse of np.repeat()?)

Question

If I have an array x, and do an np.repeat(x,2), I'm practically duplicating the array.

>>> x = np.array([1,2,3,4])    
>>> np.repeat(x, 2)
array([1, 1, 2, 2, 3, 3, 4, 4])

How can I do the opposite so that I end up with the original array?

It should also work with a random array y:

>>> y = np.array([1,7,9,2,2,8,5,3,4])

How can I delete every other element so that I end up with the following?

array([7, 2, 8, 3])

score 56 · Accepted Answer · answered Jul 21 '13 at 22:16

56

y[1::2] should do the job. Here the second element is chosen by indexing with 1, and then taken at an interval of 2.

answered Jul 21 '13 at 22:16

rafee

2

if you want y to contain this information, it should be y=y[1::2] – rafee Jul 21 '13 at 22:49

score 2 · Answer 2 · answered Oct 27 '16 at 03:40

I was having trouble with what if you asked for the input of an array by a user?

So making a function helped a lot:

def remove_every_other(my_list):
    return my_list[::2]
    pass

This helped me figure out that if any user were to enter in an array, we could handle it by calling this function.

2 Answers2