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# Python – Sort String by Custom Integer Substrings

• Last Updated : 05 Sep, 2022

Given a list of strings, sort strings by the occurrence of substring from list.

Input : test_list = [“Good at 4”, “Wake at 7”, “Work till 6”, “Sleep at 11”], subord_list = [“11”, “7”, “4”, “6”]
Output : [‘Sleep at 11’, ‘Wake at 7’, ‘Good at 4’, ‘Work till 6’]
Explanation : Strings sorted by substring presence.

Input : test_list = [“Good at 9”, “Wake at 7”, “Work till 6”, “Sleep at 11”], subord_list = [“11”, “7”, “9”, “6”]
Output : [‘Sleep at 11’, ‘Wake at 7’, ‘Good at 9’, ‘Work till 6’]
Explanation : Strings sorted by substring presence.

Method #1 : Using sorted() + zip() + lambda + regex()

The combination of above functions can be used to solve this problem. In this, we perform task of sorting by substring using regex() and sorted(), zip() is used to produce end result.

## Python3

 `# Python3 code to demonstrate working of``# Sort String by Custom Substrings``# Using sorted() + zip() + lambda + regex()``import` `re` `# initializing list``test_list ``=` `[``"Good at 4"``, ``"Wake at 7"``, ``"Work till 6"``, ``"Sleep at 11"``]` `# printing original list``print``(``"The original list : "` `+` `str``(test_list))` `# initializing substring list``subord_list ``=` `[``"6"``, ``"7"``, ``"4"``, ``"11"``]`  `# creating inverse mapping with index``temp_dict ``=` `{val: key ``for` `key, val ``in` `enumerate``(subord_list)}` `# custom sorting``temp_list ``=` `sorted``([[ele, temp_dict[re.search(``"(\d+)\$"``, ele).group()]] \``                ``for` `ele ``in` `test_list], key ``=` `lambda` `x: x[``1``])``# compiling result``res ``=` `[ele ``for` `ele ``in` `list``(``zip``(``*``temp_list))[``0``]]``        ` `# printing result``print``(``"The sorted list : "` `+` `str``(res))`

Output

```The original list : ['Good at 4', 'Wake at 7', 'Work till 6', 'Sleep at 11']
The sorted list : ['Work till 6', 'Wake at 7', 'Good at 4', 'Sleep at 11']```

Method #2 : Using sorted() + zip() + comparator + regex()

This is yet another way in which this task can be performed. In this similar functionality is used as above method, difference is that comparator function is fed to sorted() rather than lambda to sort.

## Python3

 `# Python3 code to demonstrate working of``# Sort String by Custom Substrings``# Using sorted() + comparator + regex()``import` `re` `# helper function to solve problem``def` `hlper_fnc(ele):``    ``temp ``=` `re.search(``"(\d+)\$"``, ele).group()``    ``return` `temp_dict[temp] ``if` `temp ``in` `temp_dict ``else` `int``(temp)` `# initializing list``test_list ``=` `[``"Good at 4"``, ``"Wake at 7"``, ``"Work till 6"``, ``"Sleep at 11"``]` `# printing original list``print``(``"The original list : "` `+` `str``(test_list))` `# initializing substring list``subord_list ``=` `[``"6"``, ``"7"``, ``"4"``, ``"11"``]` `# creating inverse mapping with index``temp_dict ``=` `{val: key ``for` `key, val ``in` `enumerate``(test_list)}` `# sorting using comparator``test_list.sort(key ``=` `lambda` `ele: hlper_fnc(ele))``        ` `# printing result``print``(``"The sorted list : "` `+` `str``(test_list))`

Output

```The original list : ['Good at 4', 'Wake at 7', 'Work till 6', 'Sleep at 11']
The sorted list : ['Good at 4', 'Work till 6', 'Wake at 7', 'Sleep at 11']```

The Time and Space Complexity for all the methods are the same:

Time Complexity: O(n)

Space Complexity: O(n)

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