Write a Python program to convert a list into a nested dictionary of keys

Python: Convert a list into a nested dictionary of keys

Last update on April 27 2021 12:47:55 (UTC/GMT +8 hours)

Python – Convert Lists to Nested Dictionary

Sometimes, while working with Python dictionaries, we can have a problem in which we need to convert list to nestings, i.e each list values representing new nested level. This kind of problem can have application in many domains including web development. Lets discuss certain way in which this task can be performed.

Table of Contents Show

Python: Convert a list into a nested dictionary of keys
Python – Convert Lists to Nested Dictionary
What is Python Nested Dictionary?
How to Convert a Single List to a Dictionary in Python
How to Create Nested Dictionary in Python
Nested Dictionary in Python
Examples of Nested Dictionary

Method : Using zip() + list comprehension
The combination of above functions can be combined to perform this task. In this, we iterate for zipped list and render the nested dictionaries using list comprehension.

# Python3 code to demonstrate working of 
# Convert Lists to Nestings Dictionary 
# Using list comprehension + zip() 

# initializing list 

test_list1 = ["gfg", 'is', 'best']

test_list2 = ['ratings', 'price', 'score']

test_list3 = [5, 6, 7]

# printing original list 

print("The original list 1 is : " + str(test_list1))

print("The original list 2 is : " + str(test_list2))

print("The original list 3 is : " + str(test_list3))

# Convert Lists to Nestings Dictionary 
# Using list comprehension + zip() 

res = [{a: {b: c}} for (a, b, c) in zip(test_list1, test_list2, test_list3)]

# printing result 

print("The constructed dictionary : " + str(res))

Output : The original list 1 is : ['gfg', 'is', 'best'] The original list 2 is : ['ratings', 'price', 'score'] The original list 3 is : [5, 6, 7] The constructed dictionary : [{'gfg': {'ratings': 5}}, {'is': {'price': 6}}, {'best': {'score': 7}}]

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What is Python Nested Dictionary?

A dictionary can contain another dictionary, which in turn can contain dictionaries themselves, and so on to arbitrary depth. This is known asnested dictionary.

Nested dictionaries are one of many ways to represent structured information (similar to ‘records’ or ‘structs’ in other languages).

How to Convert a Single List to a Dictionary in Python

Provided that a list is symmetric (containing equal potential key-value pairs), you can convert it to a dictionary using the for loop.

To do this, place your loop in a dictionary comprehension:

m = ["frog", "dog", "Goat", "cat"]
d = {m[a]:m[a + 1] for a in range(0, len(m), 2)}
print(d)
Output: {'frog': 'dog', 'Goat': 'cat'}

The code may look complex at first, but it actually isn't. You're only telling Python to pick a pair each time it iterates through your list. Then it should make every item on the left of each pair the key to the one on its right side, which is its value.

The integer (2) within the range parenthesis, however, ensures that your code only accepts symmetric lists.

To understand its function, change the integer from 2 to 3. Then add an item to the list before running your code.

Related: How to Run a Python Script

To achieve this without using the for loop, you can also use the built-in dict and zip functions of Python:

a = iter(m) # spin up an iterator on the list
result = dict(zip(a, a)) # Convert the iterated items into key-value pairs
print(result)
Output: {'frog': 'dog', 'Goat': 'cat'}

Unlike the looping method that you used earlier, the dict(zip()) function ignores any item without a pair.

For instance, if there are five items in a list, it ignores the fifth one and creates a matching key-value pair with the first four items:

m = ["first", "second", "third", "fourth", "fifth_odd"]
a = iter(m)
result = dict(zip(a, a))
print(result)
Output: {'first': 'second', 'third': 'fourth'}

How to Create Nested Dictionary in Python

June 27, 2021October 10, 2021 0 Comments 3 level nested dictionary python, add elements to nested dictionary python, how to access nested dictionary in python, how to create nested dictionary in python, how to create nested dictionary in python using, nested dictionary python, python create nested dictionary

In this tutorial, we are going to see how to create nested dictionary in Python. A dictionary in Python works in a similar way to a dictionary in the real world. The keys of a dictionary must be unique and have an immutable data type, such as string, integer, etc… but the values can be repeated many times and be of any type.

In Python, a dictionary is an unordered collection. For example:

dictionary = {'key1' : 'value1', 'key2': 'value2'}

What is a nested dictionary in Python?

In Python, a nested dictionary is a dictionary within another dictionary.

nested_dictionary = { 'dict_1': { 'key_1': 'value_1' }, 'dict_2': { 'key_2': 'value_2' } }

How to Create Nested Dictionary in Python

In the code below, “students” is a dictionary. Nested dictionaries 1 and 2 are assigned to the “students” dictionary. Here, the two nested dictionaries have the keys “name” and “age” with different values. Next, we display the “students” dictionary.

students = { 1: { 'name': 'Alex', 'age': '15' }, 2: { 'name': 'Bob', 'age': '29' } } print(students)

Output:

{1: {'name': 'Alex', 'age': '15'}, 2: {'name': 'Bob', 'age': '29'}}Access the elements of a nested dictionarystudents = { 1: { 'name': 'Alex', 'age': '15' }, 2: { 'name': 'Bob', 'age': '29' } } print(students[1]['name']) print(students[1]['age'])

Output:

Alex 15

Add an element to a nested dictionarystudents = { 1: { 'name': 'Alex', 'age': '15' }, 2: { 'name': 'Bob', 'age': '29' } } students[3] = {} students[3]['name'] = 'Jean' students[3]['age'] = '22' print(students[3])

Output:

{'name': 'Jean', 'age': '22'}

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Nested Dictionary in Python

In the Python programming language, we have the concept of dictionaries. The dictionaries are mutable, and we can easily add and delete the items from the dictionary. It is a collection of unordered data items.

A dictionary is consists of two parts and the first is the data set and the second one of its corresponding key value.
It also does not allow duplicates in it.
Here nested dictionary refers to the dictionary inside a dictionary.
In simple words, it refers to the dictionary, which consists of a set of multiple dictionaries.
It is used to store the data values in key-value pairs.
Nesting Dictionary means putting a dictionary inside another dictionary. Nesting is of great use as the kind of information we can model in programs is expanded greatly.
A nested dictionary contains an unordered collection of various dictionaries.
Compared with a normal dictionary, it also contains the key and its value pairs.
We can access the dictionary using its key.
A Nested dictionary can be created in Python by placing the comma-separated dictionaries enclosed within braces.
Slicing Nested Dictionary is not possible.
We can shrink or grow nested dictionaries as needed.

Syntax of Nested dictionary for adding the various dictionaries into a particular one:

Adding elements to a nested Dictionary can be done in multiple ways. One way to add a dictionary in the Nested dictionary is to add values one be one, Nesteddict[dict][key] = 'value'. Another way is to add the whole dictionary in one go, Nesteddict[dict] = { 'key': 'value'}.

Examples of Nested Dictionary

Let us understand with the help of some examples:

Example 1:

Explanation:

In the above example, we created a dictionary containing the integer key values with the corresponding string values. Here we have symbolized with the student's data in the class having roll number with the corresponding name of each student. Further, we will perform the nested operation inside this dictionary.