Python Program to extract dictionaries with maximum number of keys

Python's implementation of a data structure known more commonly as an associative array is a dictionary. A dictionary is made up of a group of key-value pairs. Each key-value combination corresponds to a key and its corresponding value.

In this article, we will learn a python program to extract dictionaries with the maximum number of keys from a list of dictionaries.

Problem Overview

Given a list containing multiple dictionaries, we need to find and extract the dictionary(ies) that have the maximum number of keys.

Example

Consider the following input list ?

inputList = [{'tutorialspoint': 10}, {'hello': 5, 'tutorialspoint': 10, 'users': 15}, {'good': 3, 'website': 9}]
print("Input:", inputList)

Input: [{'tutorialspoint': 10}, {'hello': 5, 'tutorialspoint': 10, 'users': 15}, {'good': 3, 'website': 9}]

The second dictionary {'hello': 5, 'tutorialspoint': 10, 'users': 15} has the maximum number of keys (3), so it should be extracted.

Method 1: Using for loop and len() function

This approach iterates through each dictionary and tracks the one with the maximum length using len() function ?

# input list containing dictionaries
inputList = [{'tutorialspoint': 10}, {'hello': 5, 'tutorialspoint': 10, 'users': 15},
             {'good': 3, 'website': 9}]

print("Input list of dictionaries:")
print(inputList)

# creating a new empty dictionary
resultantDict = dict()
# initializing with 0 for storing maximum length
maxLength = 0

# traversing through each element of the input list
for p in inputList:
    # checking whether the length of the current element is greater than the maximum length
    if len(p) > maxLength:
        # assigning that current element to the resultant dictionary
        resultantDict = p
        # assigning the length of a current element as the maximum length
        maxLength = len(p)

print("Resultant dictionary having maximum no of keys:")
print(resultantDict)

Input list of dictionaries:
[{'tutorialspoint': 10}, {'hello': 5, 'tutorialspoint': 10, 'users': 15}, {'good': 3, 'website': 9}]
Resultant dictionary having maximum no of keys:
{'hello': 5, 'tutorialspoint': 10, 'users': 15}

Method 2: Using list comprehension and max() function

This approach uses list comprehension to find all dictionaries with the maximum length. It returns a list containing all dictionaries that have the maximum number of keys ?

# input list containing dictionaries
inputList = [{'tutorialspoint': 10}, {'hello': 5, 'tutorialspoint': 10, 'users': 15},
             {'good': 3, 'website': 9}]

print("Input list of dictionaries:")
print(inputList)

# getting the maximum length using max() function and list comprehension
maxLength = max(len(p) for p in inputList)

# finding all dictionaries with the maximum length
resultantDict = [p for p in inputList if len(p) == maxLength]

print("Resultant dictionary having maximum no of keys:")
print(resultantDict)

Input list of dictionaries:
[{'tutorialspoint': 10}, {'hello': 5, 'tutorialspoint': 10, 'users': 15}, {'good': 3, 'website': 9}]
Resultant dictionary having maximum no of keys:
[{'hello': 5, 'tutorialspoint': 10, 'users': 15}]

Handling Multiple Dictionaries with Same Maximum Length

When multiple dictionaries have the same maximum length, the second method returns all of them ?

# input list with multiple dictionaries having same max length
inputList = [{'a': 1, 'b': 2}, {'x': 10, 'y': 20}, {'p': 100}]

maxLength = max(len(d) for d in inputList)
result = [d for d in inputList if len(d) == maxLength]

print("Dictionaries with maximum keys:", result)
print("Maximum length:", maxLength)

Dictionaries with maximum keys: [{'a': 1, 'b': 2}, {'x': 10, 'y': 20}]
Maximum length: 2

Comparison

Conclusion

Both methods effectively extract dictionaries with maximum keys. Use the for loop approach when you need a single dictionary, and list comprehension when you want all dictionaries with maximum length.