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}}}

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