Numpy round_ – Round an array to the given number of decimals.

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In this article, we focus on one of the functions of the NumPy module in Python ie Numpy round_. NumPy package mainly focuses on routines for processing of array and Numpy round_() is utilized to return the round value of array elements.

Also read: Numpy ceil – Return the ceiling of the input, element-wise

What is NumPy round_?

Numpy Round is a mathematical function of the NumPy module used in a python programming language. It is used for manipulating Numpy arrays.

To be more specific NumPy round rounds numbers. eg: np.round_(3.18) will return 3, as 3.18~3. When applied to a 1-dimensional array of numbers it will apply np.round_() to each element of the array.

Numpy Array 1d

Syntax of numpy.round_()

Note – here we have imported NumPy as np thus using its alias during implementation.

np.round(arr, decimals=0,out='none')
Parameter DescriptionRequired/Optional
arrThe input array.Required
decimalsThe number of decimal places to which the input must be roundedOptional
outalternative array to store the resultOptional
numpy.round_() syntax paramter

Return Value

An array containing all the array elements which are rounded off having the same data type as input.

Also check: NumPy around – A Complete Guide

Implementing numpy.round_()

  • If the number to be rounded is followed by a number greater than or equal to 5 ie 5,6,7,8,9 then round the number up. eg: 38 is rounded to 40 as 8>5 similarly 3.8 will be rounded as 4.
  • If the number to be rounded is followed by a number smaller than 5 ie 0,1,2,3,4 then round the number down. eg: 32 is rounded to 30 as 2>5 and similarly 4.3 will be rounded as 4.

Number Rounding 1

Examples of numpy.round_()

Importing numpy library

import numpy as np

Example 1. Rounding an array downward

Below is the code used to implement np.round_() function to calculate the round-off values of each element of the input array.

x = np.round_([1.2,3.4,5.3]) 

In the output, an array containing 3 round-off values is returned. As the numbers to be rounded is followed by a number smaller than 5, we round the number downwards.

Output :

[1. 3. 5.]

Example 2. Rounding an array upward

x = np.round_([1.6,3.5,5.8]) 

6, 5, and 8 (digits after the decimal in the input array) are greater than 5 thus leading to upward rounding of the result and we will get an output as the next integer to the float value.

Output :

[2. 4. 6.]

Example 3. Rounding a negative array

The negative sign doesn’t have an adverse effect on the rules. We can follow the same as for the positive numbers and get the nearest rounded integer.

x = np.round_([-1.2,-3.4,-5.8]) 

Output :

[-1. -3. -6.]

Example 4. Rounding an array to a specific decimal


Specifying the decimals (int the parameter decimals)allows us to manage the precision we want after rounding.

Output :

[3.42 6.74 0.5 ]


In this article, we learned the NumPy round_ function and how to utilize it to round off elements in an array to a specific decimal.