Python | Convert flattened dictionary into nested dictionary

Last Updated : 16 Aug, 2021

Given a flattened dictionary, the task is to convert that dictionary into a nested dictionary where keys are needed to be split at ‘_’ considering where nested dictionary will be started.

Method #1: Using Naive Approach

Python3

# Python code to demonstrate
# conversion of flattened dictionary
# into nested dictionary
 
 
def insert(dct, lst):
    for x in lst[:-2]:
        dct[x] = dct = dct.get(x, dict())
    dct.update({lst[-2]: lst[-1]})
     
 
def convert_nested(dct):
    # empty dict to store the result
    result = dict()
 
    # create an iterator of lists
    # representing nested or hierarchical flow
    lists = ([*k.split("_"), v] for k, v in dct.items())
 
    # insert each list into the result
    for lst in lists:
        insert(result, lst)
    return result
         
# initialising_dictionary
ini_dict = {'Geeks_for_for':1,'Geeks_for_geeks':4,
            'for_geeks_Geeks':3,'geeks_Geeks_for':7}
 
# printing initial dictionary
print ("initial_dictionary", str(ini_dict))
 
# code to convert ini_dict to nested
# dictionary splitting_dict_keys
_split_dict = [[*a.split('_'), b] for a, b in ini_dict.items()]
 
 
# printing final dictionary
print ("final_dictionary", str(convert_nested(ini_dict)))

Output:
initial_dictionary {‘for_geeks_Geeks’: 3, ‘Geeks_for_geeks’: 4, ‘geeks_Geeks_for’: 7, ‘Geeks_for_for’: 1}
final_dictionary {‘Geeks’: {‘for’: {‘for’: 1, ‘geeks’: 4}}, ‘for’: {‘geeks’: {‘Geeks’: 3}}, ‘geeks’: {‘Geeks’: {‘for’: 7}}}

Method #2: Using default dict and recursive approach

Python3

# Python code to demonstrate
# conversion of flattened dictionary
# into nested dictionary
 
# code to convert dict into nested dict
def nest_dict(dict1):
    result = {}
    for k, v in dict1.items():
         
        # for each key call method split_rec which
        # will split keys to form recursively
        # nested dictionary
        split_rec(k, v, result)
    return result
 
def split_rec(k, v, out):
     
    # splitting keys in dict
    # calling_recursively to break items on '_'
    k, *rest = k.split('_', 1)
    if rest:
        split_rec(rest[0], v, out.setdefault(k, {}))
    else:
        out[k] = v
 
         
# initialising_dictionary
ini_dict = {'Geeks_for_for':1,'Geeks_for_geeks':4,
            'for_geeks_Geeks':3,'geeks_Geeks_for':7}
 
# printing initial dictionary
print ("initial_dictionary", str(ini_dict))
 
# printing final dictionary
print ("final_dictionary", str(nest_dict(ini_dict)))

Output:
initial_dictionary {‘for_geeks_Geeks’: 3, ‘Geeks_for_for’: 1, ‘Geeks_for_geeks’: 4, ‘geeks_Geeks_for’: 7}
final_dictionary {‘for’: {‘geeks’: {‘Geeks’: 3}}, ‘geeks’: {‘Geeks’: {‘for’: 7}}, ‘Geeks’: {‘for’: {‘for’: 1, ‘geeks’: 4}}}

Method #3: Using reduce and getitem

Python3

# Python code to demonstrate
# conversion of flattened dictionary
# into nested dictionary
 
from collections import defaultdict
from functools import reduce
from operator import getitem
 
 
def getFromDict(dataDict, mapList):
     
    # Iterate nested dictionary
    return reduce(getitem, mapList, dataDict)
     
# instantiate nested defaultdict of defaultdicts
tree = lambda: defaultdict(tree)
d = tree()
 
# converting default_dict_to regular dict
def default_to_regular(d):
     
    """Convert nested defaultdict to regular dict of dicts."""
    if isinstance(d, defaultdict):
        d = {k: default_to_regular(v) for k, v in d.items()}
    return d
         
# initialising_dictionary
ini_dict = {'Geeks_for_for':1,'Geeks_for_geeks':4,
            'for_geeks_Geeks':3,'geeks_Geeks_for':7}
 
# printing initial dictionary
print ("initial_dictionary", str(ini_dict))
 
 
# code to convert ini_dict to nested dictionary
# iterating_over_dict
for k, v in ini_dict.items():
     
    # splitting keys
    * keys, final_key = k.split('_')
    getFromDict(d, keys)[final_key] = v
 
# printing final dictionary
print ("final_dictionary", str(default_to_regular(d)))

Output:
initial_dictionary {‘Geeks_for_for’: 1, ‘Geeks_for_geeks’: 4, ‘for_geeks_Geeks’: 3, ‘geeks_Geeks_for’: 7}
final_dictionary {‘Geeks’: {‘for’: {‘geeks’: 4, ‘for’: 1}}, ‘geeks’: {‘Geeks’: {‘for’: 7}}, ‘for’: {‘geeks’: {‘Geeks’: 3}}}

Attention geek! Strengthen your foundations with the Python Programming Foundation Course and learn the basics.

To begin with, your interview preparations Enhance your Data Structures concepts with the Python DS Course. And to begin with your Machine Learning Journey, join the Machine Learning – Basic Level Course

My Personal Notes

Jul	AUG	Sep
	28
2020	2021	2022

Related Articles

Python | Convert flattened dictionary into nested dictionary

Python3

Python3

Python3