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# Python – Substitute digits using Dictionary

• Last Updated : 03 Jul, 2020

Sometimes, while working with Python Dictionary, we can have a problem in which we need to perform substitution of digits of each element in List. This can lead to change in numbers. This kind of problem can occur in data preprocessing domains. Let’s discuss certain ways in which this task can be performed.

Input : test_list = [45, 32], dig_map = {4 : 2, 3 : 8, 2 : 6, 5 : 7}
Output : [27, 86]

Input : test_list = [44, 44], dig_map = {4 : 2}
Output : [22, 22]

Method #1 : Using loop
This is brute way to solve this problem. In this, we iterate through each element in list and recreate it using mapped value after converting number to string.

 `# Python3 code to demonstrate working of ``# Substitute digits using Dictionary``# Using loop `` ` `# initializing list``test_list ``=` `[``45``, ``32``, ``87``, ``34``, ``21``, ``91``] `` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# initializing digit mapping``dig_map ``=` `{``1` `: ``4``, ``4` `: ``2``, ``3` `: ``8``, ``2` `: ``6``, ``7` `: ``5``, ``9` `: ``3``, ``8` `: ``9``, ``5` `: ``7``}`` ` `# Substitute digits using Dictionary``# Using loop ``temp ``=` `[]``for` `idx, ele  ``in` `enumerate``(test_list):``    ``sub1 ``=` `str``(ele)``    ``if` `len``(sub1) > ``1``:``        ``sub2 ``=` `""``        ``for` `j ``in` `sub1:``            ``if` `int``(j) ``in` `dig_map:``                ``sub2 ``+``=` `str``(dig_map[``int``(j)])``                ``test_list[idx] ``=` `int``(sub2)``    ``else``:``        ``if` `ele ``in` `dig_map:``            ``test_list[idx] ``=` `dig_map[ele]`` ` `# printing result ``print``(``"List after Digit Substitution : "` `+` `str``(test_list))`
Output :

```The original list is : [45, 32, 87, 34, 21, 91]
List after Digit Substitution : [27, 86, 95, 82, 64, 34]
```

Method #2 : Using `join() + list comprehension + str() + int()`
The combination of above functions can be used to solve this problem. In this, we perform the task of interconversion using str() and int(), join and list comprehension are used to bind the logic in form of shorthand.

 `# Python3 code to demonstrate working of ``# Substitute digits using Dictionary``# Using join() + list comprehension + str() + int()`` ` `# initializing list``test_list ``=` `[``45``, ``32``, ``87``, ``34``, ``21``, ``91``] `` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# initializing digit mapping``dig_map ``=` `{``1` `: ``4``, ``4` `: ``2``, ``3` `: ``8``, ``2` `: ``6``, ``7` `: ``5``, ``9` `: ``3``, ``8` `: ``9``, ``5` `: ``7``}`` ` `# Substitute digits using Dictionary``# Using join() + list comprehension + str() + int()``res ``=` `[``int``(''.join([``str``(dig_map[``int``(ele)]) ``for` `ele ``in` `str``(sub)])) ``for` `sub ``in` `test_list]`` ` `# printing result ``print``(``"List after Digit Substitution : "` `+` `str``(res))`
Output :
```The original list is : [45, 32, 87, 34, 21, 91]
List after Digit Substitution : [27, 86, 95, 82, 64, 34]
```

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