Python – Case Insensitive Strings Grouping

Sometimes, we have a use case in which we need to perform the grouping of strings by various factors, like first letter or any other factor. These type of problems are typical to database queries and hence can occur in web development while programming. This article focuses on one such grouping by case insensitivity i.e grouping all strings which are same but have different cases. Let’s discuss certain ways in which this can be performed.

Method #1 : Using next() + lambda + loop
The combination of above 3 functions is used to solve this particular problem by the naive method. The lambda function performs the task of finding like cases, and next function helps in forward iteration.

# Python3 code to demonstrate
# Case Insensitive Strings Grouping
# using next() + lambda + loop

# initializing list
test_list = ['man', 'a', 'gEek', 'for', 'GEEK', 'FoR']

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

# using next() + lambda + loop
# Case Insensitive Strings Grouping
util_func = lambda x, y: str.lower(x) == str.lower(y)
res = []
for sub in test_list:
    ele = next((x for x in res if util_func(sub, x[0])), [])
    if ele == []:
        res.append(ele)
    ele.append(sub)

# print result
print("The list after Categorization : " + str(res))

Output :

The original list : ['man', 'a', 'gEek', 'for', 'GEEK', 'FoR']
The list after Categorization : [['man'], ['a'], ['gEek', 'GEEK'], ['for', 'FoR']]

Method #2 : Using sorted() + groupby()
This particular task can also be solved using the groupby function which offers a conventional method to solve this problem. The sorted function sorts the elements by size to be feed to groupby for the relevant grouping.

# Python3 code to demonstrate
# Case Insensitive Strings Grouping
# using sorted() + groupby()
from itertools import groupby

# initializing list
test_list = ['man', 'a', 'gEek', 'for', 'GEEK', 'FoR']

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

# using sorted() + groupby()
# Case Insensitive Strings Grouping
util_func = lambda x: str.lower(x)
temp = sorted(test_list, key = util_func)
res = [list(ele) for i, ele in groupby(temp, util_func)]

# print result
print("The list after Categorization : " + str(res))

Output :

The original list : ['man', 'a', 'gEek', 'for', 'GEEK', 'FoR']
The list after Categorization : [['man'], ['a'], ['gEek', 'GEEK'], ['for', 'FoR']]