Python - Sort list of lists by the size of sublists

The problem is to sort a list of lists based on the size of each sublist. For example, given the list [[1, 2], [1], [1, 2, 3]], the sorted result should be [[1], [1, 2], [1, 2, 3]] when sorted in ascending order. We will explore multiple methods to do this in Python.

Using sorted() with len()

This method uses Python's built-in sorted() function, which allows us to specify a custom key for sorting. Here, we use the length of each sublist as the key.

# Input list of lists
a = [[1, 2], [1], [1, 2, 3]]

# Sort based on sublist size
result = sorted(a, key=len)
print(result)  

[[1], [1, 2], [1, 2, 3]]

Explanation:

• sorted() function sorts the list based on a key.
• We specify len as the key, which calculates the size of each sublist.

Let's explore some more ways and see how we can sort list of lists by the size of sublists.

Using sort() with len()

If we want to sort the list in place without creating a new list, we can use the sort() method.

# Input list of lists
a = [[1, 2], [3, 4, 5], [6]]

# Sort the list in place by the size of the sublists
a.sort(key=len)
print(a)  

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

Explanation:

• sort() method modifies the original list.
• It uses the same approach as the sorted() function but works directly on the list.
• This method is slightly more memory-efficient because it avoids creating a new list.

Using List Comprehension and sorted()

We can use a combination of list comprehension and sorted() to sort the list and explicitly display the sizes of the sublists for better understanding.

# Input list of lists
a = [[1, 2], [3, 4, 5], [6]]

# Sort the list in place by the size of the sublists
a.sort(key=len)
print(a) 

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

Explanation:

• This method is a variation of the first one but explicitly uses list comprehension to emphasize the sublist selection process.
• It’s useful for demonstrating the logic but doesn’t differ significantly in efficiency.

Using For Loop

This is a more manual approach which involves iterating through the list and sorting it manually using a simple for loop.

# Input list of lists
a = [[1, 2], [3, 4, 5], [6]]

# Sort the list manually using a nested loop
for i in range(len(a)):
    for j in range(len(a) - i - 1):
        if len(a[j]) > len(a[j + 1]):
            a[j], a[j + 1] = a[j + 1], a[j]
print(a) 

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

Explanation: This method uses a bubble sort algorithm, comparing adjacent sublists and swapping them based on their size.