# Python – Rear character String categorization

• Last Updated : 27 Feb, 2020

Sometimes, we have a use case in which we need to perform the grouping of strings by various factors, like last 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 last letter of string. 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 rear character, and next function helps in forward iteration.

 `# Python3 code to demonstrate ``# Rear character String categorization``# using next() + lambda + loop `` ` `# initializing list ``test_list ``=` `[``'an'``, ``'apple'``, ``'geek'``, ``'for'``, ``'greek'``, ``'free'``] `` ` `# printing original list ``print``(``"The original list : "` `+` `str``(test_list)) `` ` `# using next() + lambda + loop ``# Rear character String categorization``util_func ``=` `lambda` `x, y: x[``len``(x) ``-` `1``] ``=``=` `y[``len``(y) ``-` `1``] ``res ``=` `[] ``for` `sub ``in` `test_list: ``    ``ele ``=` `next``((x ``for` `x ``in` `res ``if` `util_func(sub, x[``len``(x) ``-` `1``])), []) ``    ``if` `ele ``=``=` `[]: ``        ``res.append(ele) ``    ``ele.append(sub) `` ` `# print result ``print``(``"The list after Categorization : "` `+` `str``(res)) `
Output :
```The original list : ['an', 'apple', 'geek', 'for', 'greek', 'free']
The list after Categorization : [['an'], ['apple', 'free'], ['geek', 'greek'], ['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 rear character to be feed to groupby for the relevant grouping.

 `# Python3 code to demonstrate ``# Rear character String categorization``# using sorted() + groupby() ``from` `itertools ``import` `groupby `` ` `# initializing list ``test_list ``=` `[``'an'``, ``'apple'``, ``'geek'``, ``'for'``, ``'greek'``, ``'free'``] `` ` `# printing original list ``print``(``"The original list : "` `+` `str``(test_list)) `` ` `# using sorted() + groupby() ``# Rear character String categorization``util_func ``=` `lambda` `x: x[``len``(x) ``-` `1``] ``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 : ['an', 'apple', 'geek', 'for', 'greek', 'free']
The list after Categorization : [['an'], ['apple', 'free'], ['geek', 'greek'], ['for']]
```

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