Python:NumPy .sum()

The .sum() method returns the sum of array elements over a given axis. It can compute the sum of all elements or along specific axes in multi-dimensional arrays.

Syntax

ndarray.sum(axis=None, dtype=None, out=None, keepdims=False, initial=0, where=True)

Parameters:

• axis (int or tuple of ints, optional): Axis or axes along which to compute the sum. Default is None, which sums over all elements.
• dtype (data-type, optional): Type of the returned array and of the accumulator. If not specified, defaults to the data type of the array.
• out (ndarray, optional): Alternative output array to place the result.
• keepdims (bool, optional): If True, keeps the reduced dimensions with size 1. Default is False.
• initial (scalar, optional): Starting value for the sum. Default is 0.
• where (array_like of bool, optional): Elements to include in the sum. Default is True.

Return value:

Returns an ndarray containing the sum of elements. If axis is None, returns a scalar. Otherwise, returns an array with reduced dimensions.

Example 1: Sum of All Elements

In this example, the .sum() method calculates the total of all elements in the array:

import numpy as np

arr = np.array([[1, 2, 3], [4, 5, 6]])
result = arr.sum()
print(result)

Copy to clipboard
Copy to clipboard

The above code returns the following output:

21

Copy to clipboard
Copy to clipboard

Example 2: Sum Along Specific Axis

In this example, the .sum() method computes sums along specific axes, by columns (axis=0) and by rows (axis=1):

import numpy as np

arr = np.array([[1, 2, 3], [4, 5, 6]])
# Sum along axis 0 (columns)
col_sum = arr.sum(axis=0)
print("Column sums:", col_sum)

# Sum along axis 1 (rows)
row_sum = arr.sum(axis=1)
print("Row sums:", row_sum)

Copy to clipboard
Copy to clipboard

The above code returns the following output:

Column sums: [5 7 9]
Row sums: [ 6 15]

Copy to clipboard
Copy to clipboard

Here, axis=0 sums each column, and axis=1 sums each row.

Codebyte Example: Using Initial Value and where Parameter

In this example, the .sum() method demonstrates how to use an initial value for the sum and how to include elements using the where parameter:

Visit us
Visit us
Hide code
Code
Output
Hide output
Loading...
Copy to your clipboard
Copy Codebyte
Run

Note: For integer arrays, large sums may overflow. Use dtype=np.int64 or float for safe accumulation.