Sum of Elements in NumPy Array - Examples
Numpy sum()
To get the sum of all elements in a numpy array, you can use numpy.sum() function.
In this tutorial, we shall learn how to use numpy.sum() function with syntax and examples.
Syntax
The syntax of numpy.sum() is
numpy.sum(a, axis=None, dtype=None, out=None, keepdims=<no value>, initial=<no value>)
We shall understand the parameters in the function definition, using below examples.
Examples
1. Numpy sum()
In this example, we will find the sum of all elements in a numpy array, and with the default optional parameters to the sum() function.
Python Program
import numpy as np
a = np.array([4, 5, 3, 7])
print('input\n',a)
b = np.sum(a)
print('sum\n',b)
Output
input
[4 5 3 7]
sum
19
Explanation
4 + 5 + 3 + 7 = 19
2. Numpy sum() along axis
You can specify axis to the sum() and thus get the sum of the elements along an axis.
Python Program
import numpy as np
a = np.array([4, 5, 3, 7]).reshape(2, 2)
print('input\n',a)
b = np.sum(a, axis=0)
print('sum\n',b)
Output
input
[[4 5]
[3 7]]
sum
[ 7 12]
Explanation
[[4 5]
+ +
[3 7]]
------------
[7 12]
In the above program, we have found the sum along axis=0. Now, let us try with axis=1.
Python Program
import numpy as np
a = np.array([4, 5, 3, 7]).reshape(2, 2)
print('input\n',a)
b = np.sum(a, axis=1)
print('sum\n',b)
Output
input
[[4 5]
[3 7]]
sum
[ 9 10]
Explanation
[4 + 5] = 9
[3 + 7] = 10
Hence [9 10]
3. Specify an initial value to the sum
You can also specify an initial value to the sum.
By default, the initial value is 0. But, if you specify an initial value, the sum would be initial value + sum(array) along axis or total, as per the arguments.
Python Program
import numpy as np
a = np.array([4, 5, 3, 7])
print('input\n',a)
b = np.sum(a, initial=52)
print('sum\n',b)
Output
input
[4 5 3 7]
sum
71
Explanation
sum(a, initial=52) = sum(a) + initial
= sum([4 5 3 7]) + 52
= 19 + 52
= 71
Summary
In this Numpy Tutorial, we learned how to get the sum of elements in numpy array, or along an axis using numpy.sum().