numpy two dimensional array sum code example

Example 1: python how to sum columns of an array

# Example usage 1:
import numpy as np
numpy_array = np.array([[1, 2, 3, 4, 5], 
                        [1, 2, 3, 4, 5],
                        [1, 2, 3, 4, 5]])
np.sum(numpy_array, axis=0)
--> array([ 3,  6,  9, 12, 15])

# Example usage 2 (without numpy):
array = [[1, 2, 3, 4, 5],
         [1, 2, 3, 4, 5],
         [1, 2, 3, 4, 5]]
[sum(x) for x in zip(*array)]
--> [3, 6, 9, 12, 15]

Example 2: sum of a numpy array

>>> np.sum([0.5, 1.5])
2.0
>>> np.sum([0.5, 0.7, 0.2, 1.5], dtype=np.int32)
1
>>> np.sum([[0, 1], [0, 5]])
6
>>> np.sum([[0, 1], [0, 5]], axis=0)
array([0, 6])
>>> np.sum([[0, 1], [0, 5]], axis=1)
array([1, 5])
>>> np.sum([[0, 1], [np.nan, 5]], where=[False, True], axis=1)
array([1., 5.])