Python – Sort Dictionaries by Size

When working with Python dictionaries, you often need to sort them by their size (number of key-value pairs). Python provides several approaches to accomplish this using the len() function as a sorting key.

Using a Custom Function with sort()

The most straightforward approach is to define a helper function that returns the length of each dictionary ?

def get_len(element):
    return len(element)

dict_list = [
    {24: 56, 29: 11, 10: 22, 42: 28}, 
    {54: 73, 59: 11}, 
    {13: 39}, 
    {31: 22, 59: 73, 57: 44}
]

print("Original dictionary list:")
print(dict_list)

dict_list.sort(key=get_len)

print("\nSorted by size (ascending):")
print(dict_list)

Original dictionary list:
[{24: 56, 29: 11, 10: 22, 42: 28}, {54: 73, 59: 11}, {13: 39}, {31: 22, 59: 73, 57: 44}]

Sorted by size (ascending):
[{13: 39}, {54: 73, 59: 11}, {31: 22, 59: 73, 57: 44}, {24: 56, 29: 11, 10: 22, 42: 28}]

Using Lambda Function

You can achieve the same result more concisely using a lambda function ?

dict_list = [
    {24: 56, 29: 11, 10: 22, 42: 28}, 
    {54: 73, 59: 11}, 
    {13: 39}, 
    {31: 22, 59: 73, 57: 44}
]

# Sort in ascending order
dict_list.sort(key=lambda x: len(x))
print("Ascending order:")
print(dict_list)

# Sort in descending order
dict_list.sort(key=lambda x: len(x), reverse=True)
print("\nDescending order:")
print(dict_list)

Ascending order:
[{13: 39}, {54: 73, 59: 11}, {31: 22, 59: 73, 57: 44}, {24: 56, 29: 11, 10: 22, 42: 28}]

Descending order:
[{24: 56, 29: 11, 10: 22, 42: 28}, {31: 22, 59: 73, 57: 44}, {54: 73, 59: 11}, {13: 39}]

Using sorted() Function

The sorted() function creates a new sorted list without modifying the original ?

dict_list = [
    {24: 56, 29: 11, 10: 22, 42: 28}, 
    {54: 73, 59: 11}, 
    {13: 39}, 
    {31: 22, 59: 73, 57: 44}
]

# Original list remains unchanged
sorted_list = sorted(dict_list, key=len)

print("Original list:")
print(dict_list)
print("\nNew sorted list:")
print(sorted_list)

Original list:
[{24: 56, 29: 11, 10: 22, 42: 28}, {54: 73, 59: 11}, {13: 39}, {31: 22, 59: 73, 57: 44}]

New sorted list:
[{13: 39}, {54: 73, 59: 11}, {31: 22, 59: 73, 57: 44}, {24: 56, 29: 11, 10: 22, 42: 28}]

Comparison

Conclusion

Use list.sort(key=len) for in-place sorting or sorted(list, key=len) to create a new sorted list. Both methods efficiently sort dictionaries by their size using the len() function.