# NumPy sum()

Summary: in this tutorial, you’ll learn how to use the numpy `sum()` function to return the sum of all elements in an array.

## Introduction to the numpy sum() function

The numpy `sum()` function is an aggregate function that takes an array and returns the sum of all elements.

The following example uses the `sum()` function to calculate the sum of all elements of a 1-D array:

`import numpy as np`

`a = np.array([1, 2, 3]) total = np.sum(a) print(total)`

Code language: Python (python)

Output:

`6`

Code language: Python (python)

How it works.

First, create a new numpy array that has three numbers 1, 2, and 3:

`a = np.array([1, 2, 3])`

Code language: Python (python)

Second, calculate the sum of all elements in array a by using the `sum()` function:

`total = np.sum(a)`

Code language: Python (python)

Third, display the result:

`print(total)`

Code language: Python (python)

The following example uses the `sum()` function to calculate the sum of all elements of a 2-D array:

`import numpy as npa = np.array([ [1, 2, 3], [4, 5, 6] ])`

`total = np.sum(a) print(total)`

Code language: Python (python)

Output:

`21`

Code language: Python (python)

In this example, the `sum()` adds up all the numbers of the array a.

The `sum()` function also accepts the axis argument that allows you to return the sum of elements of an axis. For example:

`import numpy as npa = np.array([ [1, 2, 3], [4, 5, 6] ])`

`total = np.sum(a, axis=0) print(total)`

Code language: Python (python)

Output:

`[5 7 9]`

Code language: Python (python)

In this example, the `sum()` function returns a new array where each element is the sum of elements of the array `a` on axis-0.

Similarly, you can sum elements on axis-1 like this:

`import numpy as npa = np.array([ [1, 2, 3], [4, 5, 6] ])`

`total = np.sum(a, axis=1) print(total)`

Code language: Python (python)

Output:

`[ 6 15]`

Code language: Python (python)

## Summary

• Use the `sum()` function to get the sum of all elements of an array.
• Use the axis argument to specify the axis that you want to sum up.