Python | Convert nested dictionary into flattened dictionary

Difficulty Level : Easy
Last Updated : 14 May, 2020

Given a nested dictionary, the task is to convert this dictionary into a flattened dictionary where the key is separated by ‘_’ in case of the nested key to be started.

Given below are a few methods to solve the above task.

Method #1: Using Naive Approach

# Python code to demonstrate 
# conversion of nested dictionary 
# into flattened dictionary 
  
# code to convert ini_dict to flattened dictionary 
# default seperater '_' 
def flatten_dict(dd, separator ='_', prefix =''): 
    return { prefix + separator + k if prefix else k : v 
             for kk, vv in dd.items() 
             for k, v in flatten_dict(vv, separator, kk).items() 
             } if isinstance(dd, dict) else { prefix : dd } 
          
# initialising_dictionary 
ini_dict = {'geeks': {'Geeks': {'for': 7}}, 
            'for': {'geeks': {'Geeks': 3}}, 
            'Geeks': {'for': {'for': 1, 'geeks': 4}}} 
  
# priniting initial dictionary 
print ("initial_dictionary", str(ini_dict)) 
  
  
# printing final dictionary 
print ("final_dictionary", str(flatten_dict(ini_dict))) 

Output:

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

Method #2: Using mutuableMapping

# Python code to demonstrate 
# conversion of nested dictionary 
# into flattened dictionary 
  
from collections import MutableMapping 
  
# code to convert ini_dict to flattened dictionary 
# default seperater '_' 
def convert_flatten(d, parent_key ='', sep ='_'): 
    items = [] 
    for k, v in d.items(): 
        new_key = parent_key + sep + k if parent_key else k 
  
        if isinstance(v, MutableMapping): 
            items.extend(convert_flatten(v, new_key, sep = sep).items()) 
        else: 
            items.append((new_key, v)) 
    return dict(items) 
          
# initialising_dictionary 
ini_dict = {'geeks': {'Geeks': {'for': 7}}, 
            'for': {'geeks': {'Geeks': 3}}, 
            'Geeks': {'for': {'for': 1, 'geeks': 4}}} 
  
# priniting initial dictionary 
print ("initial_dictionary", str(ini_dict)) 
  
  
# printing final dictionary 
print ("final_dictionary", str(convert_flatten(ini_dict))) 

Output:

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

Method #3: Using Python Generators

# Python code to demonstrate 
# conversion of nested dictionary 
# into flattened dictionary 
  
my_map = {"a" : 1, 
        "b" : { 
            "c": 2, 
            "d": 3, 
            "e": { 
                "f":4, 
                6:"a", 
                5:{"g" : 6}, 
                "l":[1,"two"] 
            } 
        }} 
  
# Expected Output 
# {'a': 1, 'b_c': 2, 'b_d': 3, 'b_e_f': 4, 'b_e_6': 'a', 'b_e_5_g': 6, 'b_e_l': [1, 'two']} 
  
  
ini_dict = {'geeks': {'Geeks': {'for': 7}}, 
            'for': {'geeks': {'Geeks': 3}}, 
            'Geeks': {'for': {'for': 1, 'geeks': 4}}} 
  
# Expected Output 
# {‘Geeks_for_geeks’: 4, ‘for_geeks_Geeks’: 3, ‘Geeks_for_for’: 1, ‘geeks_Geeks_for’: 7} 
  
def flatten_dict(pyobj, keystring=''): 
    if type(pyobj) == dict: 
        keystring = keystring + '_' if keystring else keystring 
        for k in pyobj: 
            yield from flatten_dict(pyobj[k], keystring + str(k)) 
    else: 
        yield keystring, pyobj 
  
print("Input : %s\nOutput : %s\n\n" %
     (my_map, { k:v for k,v in flatten_dict(my_map) })) 
  
print("Input : %s\nOutput : %s\n\n" % 
     (ini_dict, { k:v for k,v in flatten_dict(ini_dict) })) 

Output:

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

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