# Python – Assigning Key values to list elements from Value list Dictionary

• Difficulty Level : Easy
• Last Updated : 01 Aug, 2020

Given List of elements, map them with keys of matching value from value list.

Input : test_list = [4, 6, 3, 5, 3], test_dict = {“Gfg” : [5, 3, 6], “is” : [8, 4]}
Output : [‘is’, ‘Gfg’, ‘Gfg’, ‘Gfg’, ‘Gfg’]
Explanation : 4 is present in “is” key, hence mapped in new list.

Input : test_list = [6, 3, 5, 3], test_dict = {“Gfg” : [5, 3, 6], “is” : [18, 14]}
Output : [‘Gfg’, ‘Gfg’, ‘Gfg’, ‘Gfg’]
Explanation : All elements present in “Gfg” key.

Method #1 : Using list comprehension

This is one of the ways in which this task can be performed. In this, we extract each element of dictionary value list to check list value occurrence, if matched, we assign that key’s value to that index.

## Python3

 `# Python3 code to demonstrate working of ``# Assigning Key values to list elements from Value list Dictionary``# Using list comprehension`` ` `# initializing list``test_list ``=` `[``4``, ``6``, ``3``, ``10``, ``5``, ``3``]`` ` `# printing original list``print``(``"The original list : "` `+` `str``(test_list))`` ` `# initializing dictionary ``test_dict ``=` `{``"Gfg"` `: [``5``, ``3``, ``6``], ``"is"` `: [``8``, ``4``], ``"Best"` `: [``10``, ``11``]}`` ` `# nested loop inside list comprehension to check each key ``res ``=` `[key ``for` `ele ``in` `test_list``       ``for` `key, val ``in` `test_dict.items() ``if` `ele ``in` `val]`` ` `# printing result ``print``(``"The filtered list : "` `+` `str``(res))`

Output

```The original list : [4, 6, 3, 10, 5, 3]
The filtered list : ['is', 'Gfg', 'Gfg', 'Best', 'Gfg', 'Gfg']
```

Method #2 : Using dictionary comprehension + list comprehension

This is yet another way in which this task can be performed.  In this we create inverse dictionary, and map each list value with its key, post that each key is mapped with argument key list elements for matching key value.

## Python3

 `# Python3 code to demonstrate working of ``# Assigning Key values to list elements from Value list Dictionary``# Using dictionary comprehension + list comprehension`` ` `# initializing list``test_list ``=` `[``4``, ``6``, ``3``, ``10``, ``5``, ``3``]`` ` `# printing original list``print``(``"The original list : "` `+` `str``(test_list))`` ` `# initializing dictionary ``test_dict ``=` `{``"Gfg"` `: [``5``, ``3``, ``6``], ``"is"` `: [``8``, ``4``], ``"Best"` `: [``10``, ``11``]}`` ` `# creating inverse dictionary of elements ``temp ``=` `{j : i ``for` `i, k ``in` `test_dict.items() ``for` `j ``in` `k}`` ` `# creating end result by mapping elements``res ``=` `[temp.get(key) ``for` `key ``in` `test_list]`` ` `# printing result ``print``(``"The filtered list : "` `+` `str``(res))`

Output

```The original list : [4, 6, 3, 10, 5, 3]
The filtered list : ['is', 'Gfg', 'Gfg', 'Best', 'Gfg', 'Gfg']
```

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