Python - Convert Flat dictionaries to Nested dictionary

Sometimes, while working with records, we can have a problem in which we need to perform the task of conversion of multiple flat dictionaries to a single nested dictionary. This can have applications in many domains in which data is used extensively. Let's discuss certain ways by which we can convert flat dictionaries into nested dictionaries.

Convert Flat Dictionaries to Nested dictionary in Python

Below are the ways by which we can convert flat dictionaries to nested dictionary in Python:

• Using dict() + key access
• Using zip
• Using a for loop and dictionary comprehension
• Using defaultdict() and reduce()

Convert Flattened Dictionaries to Nested dictionary 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. 

# initializing dictionaries
test_dict1 = {'gfg' : 1, 'best' : 2}
test_dict2 = {'for' : 3, 'geeks' : 5}

# printing original dictionaries
print("The original dictionary 1 is : " + str(test_dict1))
print("The original dictionary 2 is : " + str(test_dict2))

# Convert Flat dictionaries to Nested dictionary
# Using key access + dict()
res = dict()
res["level1"] = test_dict1
res['level2'] = test_dict2

# printing result 
print("The nested dictionary is : " + str(res)) 

Output:

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

Time complexity: O(1)
Auxiliary Space: O(1)

Python Convert Flat Dictionaries to Nested dictionary Using zip()

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

# initializing dictionaries
test_dict1 = {'gfg': 1, 'best': 2}
test_dict2 = {'for': 3, 'geeks': 5}

# printing original dictionaries
print("The original dictionary 1 is : " + str(test_dict1))
print("The original dictionary 2 is : " + str(test_dict2))

# Convert Flat dictionaries to Nested dictionary
# Using zip()
key_dict = ['level1', 'level2']
dict_list = [test_dict1, test_dict2]
res = dict(zip(key_dict, dict_list))

# printing result
print("The nested dictionary is : " + str(res))

Output:

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

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

Convert Flat Dictionaries to Nested dictionary Using a for loop and dictionary comprehension

In this example, flat dictionaries test_dict1 and test_dict2 are transformed into a nested dictionary res using a for loop and dictionary comprehension, associating each original dictionary with its corresponding key in the list key_dict.

# initializing dictionaries
test_dict1 = {'gfg': 1, 'best': 2}
test_dict2 = {'for': 3, 'geeks': 5}

# printing original dictionaries
print("The original dictionary 1 is : " + str(test_dict1))
print("The original dictionary 2 is : " + str(test_dict2))

# Convert Flat dictionaries to Nested dictionary
# Using a for loop and dictionary comprehension
key_dict = ['level1', 'level2']
dict_list = [test_dict1, test_dict2]

res = {}
for key, d in zip(key_dict, dict_list):
    res[key] = {k: v for k, v in d.items()}

# printing result
print("The nested dictionary is : " + str(res))

Output:

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

Time Complexity: O(n), where n is the number of items in the dictionaries.
Auxiliary Space: O(n)

Python Convert Flat Dictionaries to Nested dictionary Using defaultdict() and reduce() Functions

In this example, flat dictionaries test_dict1 and test_dict2 are transformed into a nested dictionary (nested_dict) using defaultdict, functools.reduce, and operator.setitem to iteratively update the nested structure with key-value pairs.

from collections import defaultdict
from functools import reduce
import operator

# initializing dictionaries
test_dict1 = {'gfg': 1, 'best': 2}
test_dict2 = {'for': 3, 'geeks': 5}

# printing original dictionaries
print("The original dictionary 1 is : " + str(test_dict1))
print("The original dictionary 2 is : " + str(test_dict2))

# Convert Flat dictionaries to Nested dictionary using defaultdict, functools, operators
nested_dict = defaultdict(dict)

# Combine key-value pairs into a single list
key_value_pairs = [('level1', test_dict1), ('level2', test_dict2)]

# Use functools.reduce and operator.setitem to create the nested dictionary
reduce(lambda d, kv: operator.setitem(
    d, kv[0], kv[1]) or d, key_value_pairs, nested_dict)

# Convert defaultdict to regular dictionary
nested_dict = dict(nested_dict)

# printing result
print("The nested dictionary is : " + str(nested_dict))

Output:

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