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Flattening JSON objects in Python

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  • Difficulty Level : Medium
  • Last Updated : 01 Aug, 2022

JSON(JavaScript Object Notation) is a data-interchange format that is human-readable text and is used to transmit data, especially between web applications and servers. The JSON files will be like nested dictionaries in Python. To convert a text file into JSON, there is a json module in Python. This module comes in-built with Python standard modules, so there is no need to install it externally. A flatten json is nothing but there is no nesting is present and only key-value pairs are present. 

Example:

Unflattened JSON: {‘user’ :{‘Rachel’:{‘UserID’:1717171717, ‘Email’: ‘rachel1999@gmail.com’, ‘friends’: [‘John’, ‘Jeremy’, ‘Emily’]}}} Flattened JSON: {‘user_Rachel_friends_2’: ‘Emily’, ‘user_Rachel_friends_0’: ‘John’, ‘user_Rachel_UserID’: 1717171717, ‘user_Rachel_Email’: ‘rachel1999@gmail.com’, ‘user_Rachel_friends_1’: ‘Jeremy’}

Need of flattening JSON: There are many reasons for the need of flattening JSON, such as for a better and more understandable view that is there are only key-value pairs are present without any nesting. It also allows for context-specific security and constraints to be implemented in a readable but in a more verbose way.

Approach to flatten JSON:

There are many ways to flatten JSON. There is one recursive way and another by using the json-flatten library.

Approach 1: Recursive Approach

Now we can flatten the dictionary array by a recursive approach which is quite easy to understand. The recursive approach is a bit slower than using the json-flatten library.

Example: 

Python3




# for a array value of a key
unflat_json = {'user':
               {'Rachel':
                {'UserID': 1717171717,
                 'Email': 'rachel1999@gmail.com',
                 'friends': ['John', 'Jeremy', 'Emily']
                 }
                }
               }
 
# Function for flattening
# json
 
 
def flatten_json(y):
    out = {}
 
    def flatten(x, name=''):
 
        # If the Nested key-value
        # pair is of dict type
        if type(x) is dict:
 
            for a in x:
                flatten(x[a], name + a + '_')
 
        # If the Nested key-value
        # pair is of list type
        elif type(x) is list:
 
            i = 0
 
            for a in x:
                flatten(a, name + str(i) + '_')
                i += 1
        else:
            out[name[:-1]] = x
 
    flatten(y)
    return out
 
 
# Driver code
print(flatten_json(unflat_json))


Output:

{‘user_Rachel_friends_2’: ‘Emily’, ‘user_Rachel_friends_0’: ‘John’, ‘user_Rachel_UserID’: 1717171717, ‘user_Rachel_Email’: ‘rachel1999@gmail.com’, ‘user_Rachel_friends_1’: ‘Jeremy’}

Approach 2: Using flatten_json library

The json-flatten library provides functions for flattening a JSON object to a single key-value pairs, and unflattening that dictionary back to a JSON object. Installing library In order to use the flatten_json library, we need to install this library. flatten_json can be installed by running the following command in the terminal.

pip install flatten_json

Example: 

Python3




from flatten_json import flatten
 
unflat_json = {'user':
               {'Rachel':
                {'UserID': 1717171717,
                 'Email': 'rachel1999@gmail.com',
                 'friends': ['John', 'Jeremy', 'Emily']
                 }
                }
               }
 
flat_json = flatten(unflat_json)
 
print(flat_json)


Output:

{‘user_Rachel_UserID’: 1717171717, ‘user_Rachel_Email’: ‘rachel1999@gmail.com’, ‘user_Rachel_friends_0’: ‘John’, ‘user_Rachel_friends_1’: ‘Jeremy’, ‘user_Rachel_friends_2’: ‘Emily’}


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