Python – Groups Strings on Kth character

Sometimes, while working with Python Strings, we can have a problem in which we need to perform Grouping of Python Strings on basis of its Kth character. This kind of problem can come in day-day programming. Let’s discuss certain ways in which this task can be performed. 

Method #1 : Using loop This is one way in which this task can be performed. In this, we perform the task of grouping using brute force approach. We iterate each string, and group the dictionary after conditional check using conditional statement. 

Python3

# Python3 code to demonstrate working of
# Groups Strings on Kth character
# Using loop
from collections import defaultdict

# initializing list
test_list = ["gfg", "is", "best", "for", "geeks"]

# printing original list
print("The original list is : " + str(test_list))

# initializing K
K = 2

# Groups Strings on Kth character
# Using loop
res = defaultdict(list)
for word in test_list:
    res[word[K - 1]].append(word)

# printing result
print("The strings grouping : " + str(dict(res)))

Output : 

The original list is : [‘gfg’, ‘is’, ‘best’, ‘for’, ‘geeks’] The strings grouping : {‘f’: [‘gfg’], ‘s’: [‘is’], ‘e’: [‘best’, ‘geeks’], ‘o’: [‘for’]}

Time complexity: O(n), where n is the number of elements in the test_list.
Auxiliary space: O(n), where n is the number of elements in the test_list. 

Method #2 : Using map() + loop This is yet another way to solve this problem. In this variant additional test of valid character is added using map(). 

Python3

# Python3 code to demonstrate working of
# Groups Strings on Kth character
# Using loop + map()

# initializing list
test_list = ["gfg", "is", "best", "for", "geeks"]

# printing original list
print("The original list is : " + str(test_list))

# initializing K
K = 2

# Groups Strings on Kth character
# Using loop + map()
res = dict()
for char in map(chr, range(97, 123)):
    words = [idx for idx in test_list if idx[K - 1] == char]
    if words:
        res[char] = words

# printing result
print("The strings grouping : " + str(res))

Output : 

The original list is : [‘gfg’, ‘is’, ‘best’, ‘for’, ‘geeks’] The strings grouping : {‘f’: [‘gfg’], ‘s’: [‘is’], ‘e’: [‘best’, ‘geeks’], ‘o’: [‘for’]}

Time Complexity: O(n*n) where n is the number of elements in the dictionary. The  map() + loop is used to perform the task and it takes O(n*n) time.
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the dictionary.