Fast way to take average of every N rows in a .npy array

Question

I have a very large masked NumPy array (originalArray) with many rows and two columns. I want take the average of every two rows in originalArray

Answer 1

import numpy as np

def av(array):
    return  1. * np.sum(array.reshape(1. * array.shape[0] / 2,2, array.shape[1]),axis = 1) / array.shape[1]

a = np.array([[1,1],[2,2],[3,3],[4,4]])

print av(a)

>> [[ 1.5  1.5] [ 3.5  3.5]]