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Python – Unlist Single Valued Dictionary List

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Given a list of dictionaries, perform the unlisting of records in which we just have 1 dictionary as record element.

Input : test_list = [{'best': [{'a': 6}], 'Gfg': 15}] 
Output : [{'best': {'a': 6}, 'Gfg': 15}] 
Explanation : The value list associated with 'best' key is changed to dictionary.
Input : test_list = [{'Gfg': [{'best' : 17}]}] 
Output : [{'Gfg': {'best': 17}}] 
Explanation : 'Gfg' key's value changed to single dictionary.

Method #1: Using loop + isinstance() 

This is a brute-force way in which this task can be performed. In this, we test for the list type using isinstance(), and loop is used for iterations.

Python3




# Python3 code to demonstrate working of
# Unlist Single Valued Dictionary List
# Using loop + isinstance()
 
# Initializing list
test_list = [{'Gfg': 1,
            'is': [{'a': 2, 'b': 3}]},
            {'best': [{'c': 4, 'd': 5}],
             'CS': 6}]
 
# Printing original list
print("The original list is : " + str(test_list))
 
# Using loop + isinstance()
for dicts in test_list:
    for key, val in dicts.items():
         
        # Checking for list to convert
        # isinstance() function
        if isinstance(val, list):
            dicts[key] = val[0]
 
# Printing result
print("The converted Dictionary list : " + str(test_list))


Output : 

The original list is : [{'Gfg': 1, 'is': [{'b': 3, 'a': 2}]}, {'CS': 6, 'best': [{'d': 5, 'c': 4}]}]
The converted Dictionary list : [{'Gfg': 1, 'is': {'b': 3, 'a': 2}}, {'CS': 6, 'best': {'d': 5, 'c': 4}}]

 

Time complexity: O(N*M), where n is the length of the outer list and m is the maximum length of a list inside the dictionaries of the outer list.
Auxiliary Space: O(1), since the program does not create any additional data structures proportional to the input size. It only modifies the existing list in place.

Method #2: Using list comprehension + isinstance()

The combination of the above functions can be used to solve the problem. In this, we perform a similar task with a shorthand approach similar to the above method.

Python3




# Python3 code to demonstrate working of
# Unlist Single Valued Dictionary List
# Using list comprehension + isinstance()
 
# Initializing list
test_list = [{'Gfg': 1,
              'is': [{'a': 2, 'b': 3}]},
             {'best': [{'c': 4, 'd': 5}],
              'CS': 6}]
 
# Printing original list
print("The original list is : " + str(test_list))
 
# Similar way as above, extracting first element of list
# using list comprehension + isinstance() function
res = [{key: val[0] if isinstance(val, list) else val
 
        for key, val in sub.items()}
       for sub in test_list]
 
# Printing the result
print("The converted Dictionary list : " + str(res))


Output : 

The original list is : [{'Gfg': 1, 'is': [{'b': 3, 'a': 2}]}, {'CS': 6, 'best': [{'d': 5, 'c': 4}]}]
The converted Dictionary list : [{'Gfg': 1, 'is': {'b': 3, 'a': 2}}, {'CS': 6, 'best': {'d': 5, 'c': 4}}]

 

Time complexity: O(N*M), where n is the length of the outer list and m is the maximum length of a list inside the dictionaries of the outer list.
Auxiliary Space: O(N), where n is the number of elements in the list “test_list”.

Method 3: Using a nested for loop and checking the type of the value.

Python3




# Python3 code to demonstrate working of
# Unlist Single Valued Dictionary List
# Using nested for loop
 
# Initializing list
test_list = [{'Gfg': 1,
              'is': [{'a': 2, 'b': 3}]},
             {'best': [{'c': 4, 'd': 5}],
              'CS': 6}]
 
# Printing original list
print("The original list is : " + str(test_list))
 
# Using nested for loop
res = []
 
for sub in test_list:
    temp = {}
     
    for key, val in sub.items():
        if isinstance(val, list) and len(val) == 1 and isinstance(val[0], dict):
            temp[key] = val[0]
        else:
            temp[key] = val
    res.append(temp)
 
# Printing result
print("The converted Dictionary list : " + str(res))


Output

The original list is : [{'Gfg': 1, 'is': [{'a': 2, 'b': 3}]}, {'best': [{'c': 4, 'd': 5}], 'CS': 6}]
The converted Dictionary list : [{'Gfg': 1, 'is': {'a': 2, 'b': 3}}, {'best': {'c': 4, 'd': 5}, 'CS': 6}]

Time complexity: O(NM) where N is the number of dictionaries in the list and M is the maximum number of keys in a dictionary. 
Auxiliary space: O(NM) because we are creating a new list of dictionaries with the same number of keys and values as the original list.

Method 4: Using recursion to flatten and unlist the dictionary list

Approach:

  1. Define a function that takes a dictionary or list as input and returns the flattened and unlisted version of it.
  2. Check if the input is a dictionary. If it is, then iterate over its keys and values.
  3. If the value is a dictionary or list, call the function recursively on that value to flatten and unlist it.
  4. If the value is a list with only one element, then return that element.
  5. If the value is not a dictionary or list, return the value.
  6. If the input is a list, then iterate over its elements and call the function recursively on each element.
  7. Return the flattened and unlisted list.

Python3




# Python3 code to demonstrate working of
# Unlist Single Valued Dictionary List
# Using recursion
 
# Initializing list
test_list = [{'Gfg': 1,
              'is': [{'a': 2, 'b': 3}]},
             {'best': [{'c': 4, 'd': 5}],
              'CS': 6}]
 
# Printing original list
print("The original list is : " + str(test_list))
 
# Flatten and Unlisting the dictionary list
# Using recursion
def unlist_dict_list(input):
 
    if isinstance(input, dict):
        return {key: unlist_dict_list(val) for key, val in input.items()}
    elif isinstance(input, list):
        if len(input) == 1:
            return unlist_dict_list(input[0])
        else:
            return [unlist_dict_list(elem) for elem in input]
    else:
        return input
 
 
res = unlist_dict_list(test_list)
 
# Printing the resultant list
print("The converted Dictionary list : " + str(res))


Output

The original list is : [{'Gfg': 1, 'is': [{'a': 2, 'b': 3}]}, {'best': [{'c': 4, 'd': 5}], 'CS': 6}]
The converted Dictionary list : [{'Gfg': 1, 'is': {'a': 2, 'b': 3}}, {'best': {'c': 4, 'd': 5}, 'CS': 6}]

Time complexity: O(N), where n is the total number of elements in the dictionary list.
Auxiliary space: O(N), where n is the total number of elements in the dictionary list.



Last Updated : 03 May, 2023
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