numpy summing rows code example

Example 1: python get a vector of row sums from an array

# Basic syntax:
np.sum(your_array, axis=1).tolist()
# Where axis=1 sums across rows and axis=0 sums across columns

# Example usage:
import numpy as np
your_array = np.array([range(0,4),range(3,7),range(1,5),range(2,6)])
print(your_array)
--> [[0 1 2 3]
 	 [3 4 5 6]
     [1 2 3 4]
     [2 3 4 5]]

np.sum(your_array, axis=0).tolist() # Return column sums
--> [6, 10, 14, 18]
np.sum(your_array, axis=1).tolist() # Return row sums
--> [6, 18, 10, 14]

Example 2: 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]