How can I sum every n array values and place the result into a new array? [duplicate]

Answer 1

Cut the array to the correct length first then do a reshape.

import numpy as np

N = 3
a = np.array([1,2,3,4,5,6,7,8,1,2,3,4,5,6,7,8])


# first cut it so that lenght of a % N is zero
rest = a.shape[0]%N
a = a[:-rest]


assert a.shape[0]%N == 0


# do the reshape
a_RS = a.reshape(-1,N)
print(a_RS)

>> [[1 2 3]
    [4 5 6]
    [7 8 1]
    [2 3 4]
    [5 6 7]]

then you can simply add it up:

print(np.sum(a_RS,axis=1))

>> [ 6 15 16  9 18]