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

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