Summing elements in a sliding window - NumPy

2020-07-01

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Question

There is a numpy way to make a sum each three elements in the interval? For example:

import numpy as np
mydata = np.array([4, 2, 3, 8, -6, 10])

I would like to get this result:

np.array([9, 13, 5, 12])

Answer

A solution without using external libraries might look like this:

from collections import deque
def sliding_window_sum(a, size):
  out     = []
  the_sum = 0
  q       = deque()
  for i in a:
    if len(q)==size:
      the_sum -= q[0]
      q.popleft()
    q.append(i)
    the_sum += i
    if len(q)==size:
      out.append(the_sum)
  return out
v = [0, 0, 0, 0, 1, 1, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1]
sliding_window_sum(v, 5)

Which gives the output:

[1, 2, 3, 3, 4, 4, 3, 2, 3, 2, 1, 1, 1, 0, 0, 1]

This matches the result of using numpy:

import numpy as np
np.convolve(v, np.ones(5, dtype=int),'valid').tolist()