Python – Convert Flat dictionaries to Nested dictionary

Sometimes, while working with records, we can have problem in which we need to perform the task of conversion of multiple flat dictionaries to a single nested dictionary. This can have application in many domains in which data is used extensively. Lets discuss certain ways in which this task can be performed. 

Method #1 : Using dict() + key access This is one of the way in which this task can be performed. In this, we construct empty dictionary using dict and assign a new level to dictionary using manual brute key access. 

Time complexity: O(1) – constant time complexity, as the input size is fixed and the operations performed on it are not dependent on the input size.
Auxiliary Space: O(1) – constant auxiliary space complexity, as the size of the output dictionary is fixed and the memory used to store it is not dependent on the input size.

Method #2 : Using zip() This is another way in which this task can be performed. In this we link inner keys to outer keys using zip(). 

Time complexity: O(n), where n is the number of values in the dictionary.
Auxiliary Space: O(1), constant extra space is required

Method #3: Using a for loop and dictionary comprehension

Step-by-step approach:

• Initialize dictionaries test_dict1 and test_dict2 with key-value pairs.
• Print the original dictionaries using the print() function.
• Create a list key_dict containing the key names of the levels we want to create in the nested dictionary.
• Create a list dict_list containing the original dictionaries we want to convert.
• Use a for loop and dictionary comprehension to create a nested dictionary by iterating through the key_dict list and using each item as a key name for the current dictionary in the dict_list. The dictionary comprehension creates a new key-value pair in the nested dictionary for each key-value pair in the current dictionary.
  • Assign the nested dictionary to a variable called res.
• Print the result using the print() function.

Below is the implementation of the above approach:

The original dictionary 1 is : {'gfg': 1, 'best': 2}
The original dictionary 2 is : {'for': 3, 'Lazyroar': 5}
The nested dictionary is : {'level1': {'gfg': 1, 'best': 2}, 'level2': {'for': 3, 'Lazyroar': 5}}

Time Complexity: O(n), where n is the number of items in the dictionaries.
Auxiliary Space: O(n), since we are creating a new nested dictionary with the same number of items as the original dictionaries.