How to Round A Number to Significant Digits in Python

1. Use the round() Function to Round a Number to the Given Significant Digit in Python
2. Use the math Module to Round a Number to the Given Significant Digit in Python
3. Use String Formatting to Round a Number to the Given Significant Digit in Python
4. Use the sigfig Module to Round a Number to the Given Significant Digit in Python
5. Use the decimal Module to Round a Number to the Given Significant Digit in Python
6. Use NumPy to Round a Number to the Given Significant Digit in Python

Rounding the number means replacing a number with an approximate value that is close to it. We can also round numbers to the required significant figure.

In this article, we will round a number to a specific significant digit in Python.

Use the round() Function to Round a Number to the Given Significant Digit in Python

The round() function rounds the given floating values to the nearest integer or specified decimal position.

We can use a negative number to round the integer to the significant floor value by assigning it to the round() function. This negative number to be specified depends on the required significant digits.

For example, if we wish to round to one significant digit, we specify the value as (1-total digits) in the round() function.

See the following code.

x = round(1342, -3)
print(x)

Output:

1000

Use the math Module to Round a Number to the Given Significant Digit in Python

This method is an improvement on the previously discussed function. We can create a simple user-defined function to make this more convenient. We won’t have to specify the negative number in this method’s round() function. We will replace this using a combination of the math.floor() function and the math.log10() function.

See the code below.

from math import log10, floor


def round_it(x, sig):
    return round(x, sig - int(floor(log10(abs(x)))) - 1)


print(round_it(1324, 1))

Output:

1000

Use String Formatting to Round a Number to the Given Significant Digit in Python

In Python, the %g specifier in string formats a float rounded to a specified significant figure. If the magnitude of the final number is huge, then it shows it in scientific notation.

This method returns a string. So, we have to convert the string number back to a float or integer value after formatting it.

For example,

x = float("%.1g" % 1324)
print(x)

Output:

1000.0

Use the sigfig Module to Round a Number to the Given Significant Digit in Python

The sigfig module is the best fit for rounding the numbers to a significant digit as it minimizes the hassle of creating a user-defined function and simplifies the code.

We can specify the number of significant digits in this module’s round() function.

See the following example.

from sigfig import round

print(round(1324, sigfigs=1))

Output:

1000

Use the decimal Module to Round a Number to the Given Significant Digit in Python

The decimal module introduces a robust set of tools for high-precision decimal arithmetic and intricate rounding options. To round a number to a specific significant digit, we can leverage the scaleb() method from the decimal module.

Example Codes

from decimal import Decimal, ROUND_HALF_UP
import math


def round_to_significant_digit(number, digits):
    scaled_number = Decimal(str(number)).scaleb(
        -int(math.floor(math.log10(abs(number)))) + (digits - 1)
    )
    rounded_number = scaled_number.quantize(Decimal("1"), rounding=ROUND_HALF_UP)
    return float(rounded_number)


rounded_number = round_to_significant_digit(1324, 1)
print(rounded_number)

Output:

1000.0

In the provided example:

• Decimal(str(number)) converts the input number to a Decimal object, ensuring precision.
• scaleb() method is used to scale the number to the desired significant digit. The scaling factor is calculated using the formula -int(math.floor(math.log10(abs(number)))) + (digits - 1).
• quantize() method is employed to round the scaled number to the nearest integer while adhering to rounding rules specified by ROUND_HALF_UP.

Use NumPy to Round a Number to the Given Significant Digit in Python

NumPy, a powerful numerical computing library, offers a versatile function for rounding numbers to a specified number of significant digits. The numpy.around() function serves as a valuable tool for this purpose.

Example

import numpy as np


def round_to_significant_digit(number, digits):
    rounded_number = np.around(
        number, digits - int(np.floor(np.log10(abs(number)))) - 1
    )
    return rounded_number


rounded_number = round_to_significant_digit(1324, 1)
print(rounded_number)

Output:

1000.0

In the provided example:

• np.around() function is used to round the number to the specified significant digit. The rounding precision is calculated using digits - int(np.floor(np.log10(abs(number)))) - 1.