How to Sort a Dictionary in Python

How to Sort a Dictionary in Python

A robust data structure for storing key-value pairs is a Python dictionary. They are mutable, meaning their contents can be modified after creation. However, dictionaries are inherently unordered, which means the data is not stored in a specific sequence.

While a dictionary permits duplicate values, each key must be distinct. Dictionaries are declared using curly braces {}, with key-value pairs separated by commas.

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Example:

student_info = {'name': 'Devansh', 'age': 22, 'Rollno': 90014}
print(student_info)

Output:

{'name': 'Devansh', 'age': 22, 'Rollno': 90014}

Why Is Sorting a Dictionary Necessary?

Sorting dictionaries can be helpful in various scenarios:

• The search time complexity of a list is O(n), while dictionaries offer O(1) lookup time, making them faster for key-based searches.
• Sorting helps in analyzing data efficiently when working with data structures.
• A sorted dictionary improves readability and simplifies complex operations.

Methods to Sort a Dictionary:

1. Sorting by Keys
2. Sorting by Values
3. Using Custom Sorting Algorithms
4. Reversing the Sorted Order

1. Sorting a Dictionary by Keys

Python provides built-in functions like keys() and items() to sort a dictionary based on its keys.

Example:

names = {1: 'Alice', 2: 'John', 4: 'Peter', 3: 'Andrew', 6: 'Ruffalo', 5: 'Chris'}  
# Print sorted keys
print(sorted(names.keys()))  
# Print sorted dictionary items
print(sorted(names.items()))

Output:

[1, 2, 3, 4, 5, 6]
[(1, 'Alice'), (2, 'John'), (3, 'Andrew'), (4, 'Peter'), (5, 'Chris'), (6, 'Ruffalo')]

Explanation:

• The dictionary keys are arranged in ascending order using the sorted() function.
• The sorted dictionary can be obtained as key-value tuples by using items().

2. Sorting a Dictionary by Values

To sort the dictionary according to values, we can combine a lambda function with the sorted() method.

Example:

dict_scores = {'Alice': 85, 'John': 92, 'Peter': 78, 'Andrew': 90}  
# Sort by values
sorted_scores = dict(sorted(dict_scores.items(), key=lambda x: x[1]))  
print(sorted_scores)

Output:

{'Peter': 78, 'Alice': 85, 'Andrew': 90, 'John': 92}

Explanation:

• The sorted() function sorts based on the second element (value) of each key-value pair using lambda x: x[1].
• The outcome is then transformed back into a dictionary.

3. Sorting a Dictionary Using Custom Algorithms

For more individualized sorting, Python lets us utilize additional arguments in the sorted() function.

Example:

daynames = {'one': 'Monday', 'six': 'Saturday', 'three': 'Wednesday', 'two': 'Tuesday', 'five': 'Friday', 'seven': 'Sunday'}  
print(daynames)  
number = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5, 'six': 6, 'seven': 7}  
print(sorted(daynames, key=number.__getitem__))  
print([daynames[i] for i in sorted(daynames, key=number.__getitem__)])

Output:

{'one': 'Monday', 'six': 'Saturday', 'three': 'Wednesday', 'two': 'Tuesday', 'five': 'Friday', 'seven': 'Sunday'}
['one', 'two', 'three', 'five', 'six', 'seven']
['Monday', 'Tuesday', 'Wednesday', 'Friday', 'Saturday', 'Sunday']

Explanation:

• The dictionary is sorted based on a predefined numbering of days.
• We use number.__getitem__ to define the sorting order.

4. Reversing the Sorted Order

By using the reverse=True argument, we can sort dictionaries in descending order.

Example:

a = {'a': 2, 'b': 1, 'c': 3, 'd': 4, 'e': 5, 'f': 6}  
print(sorted(a.values(), reverse=True))

Output:

[6, 5, 4, 3, 2, 1]

Explanation:

• reverse=True ensures that the sorted values appear in descending order.

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Conclusion

Sorting a dictionary in Python is an essential skill when dealing with large datasets. Whether you sort by keys, values, or use custom sorting logic, Pythons built-in functions make it easy to manipulate dictionaries efficiently. By mastering dictionary sorting, you can improve the performance and readability of your Python applications.

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