[Tut] 5 Effective Methods to Sort a List of String Numbers Numerically in Python

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[Tut] 5 Effective Methods to Sort a List of String Numbers Numerically in Python

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Problem Formulation

Sorting a list of string numbers numerically in Python can lead to unexpected issues.

For example, using the naive approach to sort the list

Code:

lst = ["1", "10", "3", "22", "23", "4", "2", "200"]

using

Code:

lst.sort()

will result in the incorrect order as it sorts the list of strings lexicographically, not numerically.

In this short article, my goal is to present the five best methods to correctly sort this list numerically. My recommended approach is the fifth one, see below.

Method 1: Convert Strings to Integers and Sort

This method involves converting each string in the list to an integer and then sorting them. It’s a direct and simple approach to ensure numerical ordering.

Code:

lst = [int(x) for x in lst] lst.sort()

Output:

Code:

['1', '2', '3', '4', '10', '22', '23', '200']

Recommended: Python List Comprehension

Method 2: Using the

Code:

key

Parameter with sort()

This method uses the

Code:

key

parameter with the

Code:

int

function to sort the strings as integers. It allows for numerical comparison without altering the original strings.

Code:

lst.sort(key=int)

Output:

Code:

['1', '2', '3', '4', '10', '22', '23', '200']

Recommended: Python

Code:

list.sort()

with key parameter

Method 3: Using the natsort Module

The

Code:

natsort

module provides a natural sorting algorithm, useful for sorting strings that represent numbers. This method can handle more complex string sorting scenarios.

Code:

from natsort import natsorted lst = natsorted(lst)

Output:

Code:

['1', '2', '3', '4', '10', '22', '23', '200']

Method 4: Using Regular Expressions

Using regular expressions, this method can sort strings containing both letters and numbers. It converts the numeric parts into floats for comparison, handling mixed content.

Code:

import re def sort_human(l): convert = lambda text: float(text) if text.isdigit() else text alphanum = lambda key: [convert(c) for c in re.split('([-+]?[0-9]*\.?[0-9]*)', key)] l.sort(key=alphanum) return l lst = sort_human(lst)

Output:

Code:

['1', '2', '3', '4', '10', '22', '23', '200']

Recommended: Python Regular Expression Superpower

Method 5: Using sorted() with key Parameter (Recommended)

This method combines the simplicity of using the

Code:

key

parameter with the benefit of creating a new sorted list, leaving the original untouched. It’s concise and effective.

Code:

lst = sorted(lst, key=int)

Output:

Code:

['1', '2', '3', '4', '10', '22', '23', '200']

Recommended: Python

Code:

sorted()

function

Summary – When to Use Which

• Method 1: Converts strings to integers, then sorts. Simple but alters the original list.
  
  
• Method 2: Uses the
  Code:

  key
  parameter with
  Code:

  int
  for sorting. Preserves the original strings.
  
  
• Method 3: Utilizes the
  Code:

  natsort
  module. Handles complex scenarios.
  
  
• Method 4: Employs regular expressions for sorting alphanumeric strings.
  
  
• Method 5 (Recommended): Combines the simplicity of using
  Code:

  key
  with
  Code:

  sorted()
  . Preserves the original list and offers concise code.
  

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