Python | Sort given list of strings by part of string

We are given with a list of strings, the task is to sort the list by part of the string which is separated by some character. In this scenario, we are considering the string to be separated by space, which means it has to be sorted by second part of each string.

Using sort() with lambda function

This method uses the list.sort() function to sort the list in place and while sorting it applies it uses a lambda function to extract the second word from each string as the sorting key.

li = ["GeeksForGeeks abc", "manjeet xab", "akshat bac"]

# Sorting the list in place using a lambda function
li.sort(key=lambda s: s.split()[1])

print("Sorted list:", li)

Sorted list: ['GeeksForGeeks abc', 'akshat bac', 'manjeet xab']

Explanation: sort() function sorts the list li in-place and the key parameter is a lambda function that splits each string in the list by spaces and uses the second part (x.split()[1]) as key for sorting.

Using sorted()

This method is very similar to the "Using sort with Lambda " method given above but only difference between two methods is that sorted() returns a new sorted list without modifying the original while sort() sorts the list in-place and doesn't return anything.

li = ["GeeksForGeeks abc", "manjeet xab", "akshat bac"]

# Sorting based on the second word
res = sorted(li, key=lambda x: x.split()[1])

print(res)

['GeeksForGeeks abc', 'akshat bac', 'manjeet xab']

Using itemgetter() method

In this method we use itemgetter() method to fetch the second part of each string after splitting, and sort the list based on that part.

from operator import itemgetter

li = ["GeeksForGeeks abc", "manjeet xab", "akshat bac"]

# Sorting using itemgetter for the second part
res = sorted(li, key=lambda x: itemgetter(1)(x.split()))

print(res)

['GeeksForGeeks abc', 'akshat bac', 'manjeet xab']

Explanation: itemgetter(1) is used to retrieve the second part of each split string (after the space) and then lambda function defined by [ lambda x: itemgetter(1)(x.split()) ] sorts the list based on this second part.

Using Regular Expressions

This approach uses the re.findall() function from the re module to extract the last word of each string and then sorts the list using the extracted words as the key.

import re

li = ['GeeksForGeeks abc', 'manjeet xab', 'akshat bac']
regex = r'\w+$'  # matches the last word of the string

# Sorting based on the last word using regular expression
res = sorted(li, key=lambda x: re.findall(regex, x)[0])

print(res)

['GeeksForGeeks abc', 'akshat bac', 'manjeet xab']

Explanation:

• re.findall(regex, x) finds the last word in each string based on the regex pattern "\w+$"
• lambda x: re.findall(regex, x)[0], is lambda function that sorts the list using the extracted last word.

Using Counter Method with defaultdict

It uses defaultdict to group strings by their second part without worrying about missing keys and then combines the sorted groups using list comprehension.

from collections import defaultdict

li = ['GeeksForGeeks abc', 'manjeet xab', 'akshat bac']

# Grouping by second part
d = defaultdict(list)
for s in li:
    substr = s.split()[1]
    d[substr].append(s)

# Sorting and combining the result
res = [s for substr in sorted(d.keys()) for s in d[substr]]

print(res)

['GeeksForGeeks abc', 'akshat bac', 'manjeet xab']

Explanation: d[substr].append(s) groups strings by their second word and sorted(d.keys()) is used to sort these groups, then the final list is constructed using list comprehension to combine the sorted groups.