Sort given list of strings by part the numeric part of string - Python

Last Updated : 10 Apr, 2025

We are given a list of strings containing both letters and numbers, and the goal is to sort them based on the numeric part within each string. To do this, we extract the digits, convert them to integers and use them as sorting keys. For example, in ["Gfg34", "is67", "be3st"], the numbers 34, 67, and 3 are extracted and used for sorting. Let's explore different ways to implement this in Python.

Using re.search()

re.search() from the re module searches for the first occurrence of a pattern in a string. To extract digits, a pattern like \d+ is used, which matches one or more consecutive digits. It helps directly find and retrieve numeric substrings embedded within text.

Python

import re
a = ["Gfg34", "is67", "be3st", "f23or", "ge9eks"]

res = sorted(a, key=lambda x: int(re.search(r'\d+', x).group()))
print(res)

Output

['be3st', 'ge9eks', 'f23or', 'Gfg34', 'is67']

Explanation: re.search(r'\d+', x) finds the first sequence of digits in each string and .group() extracts it as a string. This is then converted to an integer and used as the sorting key in sorted(), allowing the list to be ordered by the numeric parts of the strings.

Using filter(str.isdigit)

filter() iterate over each character in a string, keeping only the ones where str.isdigit() returns True. The result is a sequence of digit characters, which can be joined to form a complete number string. It's a clean, built-in alternative to manual loops for digit extraction.

Python

a = ["Gfg34", "is67", "be3st", "f23or", "ge9eks"]

res = sorted(a, key=lambda x: int(''.join(filter(str.isdigit, x))))
print(res)

Output

['be3st', 'ge9eks', 'f23or', 'Gfg34', 'is67']

Explanation: filter(str.isdigit, x) picks out all digits from each string and ''.join() combines them into a number string. This is converted to an integer and used as the sorting key, so the list is sorted based on the numbers inside the strings.

Using tuple pairing

Tuple pairing is a technique where each string is paired with its numeric part (extracted using logic like regex or filter(str.isdigit)). These (number, string) tuples are then sorted by the numeric key. Since Python sorts tuples by the first element, this ensures strings are sorted based on the numbers within them.

Python

def fun(s):
    num = ''
    for ch in s:
        if ch.isdigit():
            num += ch
    return int(num)

a = ["Gfg34", "is67", "be3st", "f23or", "ge9eks"]

res = sorted(a, key=fun)
print(res)

Output

['be3st', 'ge9eks', 'f23or', 'Gfg34', 'is67']

Explanation: fun() function goes through each character in a string s, collects all digits, and forms a number. It returns this number as an integer. The sorted() function uses this number as the sorting key, so the strings in list a are sorted based on their numeric parts.