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Python | Merge Python key values to list

  • Last Updated : 02 Aug, 2019
Geek Week

Sometimes, while working with Python, we might have a problem in which we need to get the values of dictionary from several dictionaries to be encapsulated into one dictionary. This type of problem can be common in domains in which we work with relational data like in web developments. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using setdefault() + loop
This task can be performed using a nested loop and fetching each element of dictionary and creating a new list to new key or appending the values in case of similar key occurrence.




# Python3 code to demonstrate working of
# Merge Python key values to list
# Using setdefault() + loop
  
# Initialize list
test_list = [{'gfg' : 2, 'is' : 4, 'best' : 6}, 
             {'it' : 5, 'is' : 7, 'best' : 8},
             {'CS' : 10}]
  
# Printing original list
print("The original list is : " + str(test_list))
  
# using setdefault() + loop
# Merge Python key values to list
res = {}
for sub in test_list:
    for key, val in sub.items(): 
        res.setdefault(key, []).append(val)
  
# printing result 
print("The merged values encapsulated dictionary is : " + str(res))
Output :

The original list is : [{‘is’: 4, ‘gfg’: 2, ‘best’: 6}, {‘it’: 5, ‘is’: 7, ‘best’: 8}, {‘CS’: 10}]
The merged values encapsulated dictionary is : {‘is’: [4, 7], ‘it’: [5], ‘gfg’: [2], ‘CS’: [10], ‘best’: [6, 8]}

 



Method #2 : Using list comprehension + dictionary comprehension
The combination of above can be used to perform this particular task. This offers a one liner that can be employed for this task. Even though it might be efficient on performance domain.




# Python3 code to demonstrate working of
# Merge Python key values to list
# Using list comprehension + dictionary comprehension
  
# Initialize list
test_list = [{'gfg' : 2, 'is' : 4, 'best' : 6}, 
             {'it' : 5, 'is' : 7, 'best' : 8},
             {'CS' : 10}]
  
# Printing original list
print("The original list is : " + str(test_list))
  
# using list comprehension + dictionary comprehension
# Merge Python key values to list
res = {key: list({sub[key] for sub in test_list if key in sub})
      for key in {key for sub in test_list for key in sub}}
  
# printing result 
print("The merged values encapsulated dictionary is : " + str(res))
Output :

The original list is : [{‘is’: 4, ‘gfg’: 2, ‘best’: 6}, {‘it’: 5, ‘is’: 7, ‘best’: 8}, {‘CS’: 10}]
The merged values encapsulated dictionary is : {‘is’: [4, 7], ‘it’: [5], ‘gfg’: [2], ‘CS’: [10], ‘best’: [6, 8]}

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