💡 Problem Formulation: In various coding scenarios, we need to sort lists where elements have several digits. The requirement that complicates the task is when the sorting is based on the maximum digit contained in each element, not on the element’s value itself. For example, given an input list [123, 45, 299, 38], the desired output after sorting based on the highest digit should be [123, 38, 45, 299].
Method 1: Using a Custom Key Function
This method involves defining a custom key function, which is passed to Python’s built-in sorted() function. The key function extracts the highest digit in each element to guide the sorting.
Here’s an example:
def max_digit(num):
return int(max(str(num)))
numbers = [123, 45, 299, 38]
sorted_numbers = sorted(numbers, key=max_digit)
print(sorted_numbers)Output: [123, 38, 45, 299]
This function converts each number to a string then iterates over each character (digit) to find the maximum, which is then converted back to an integer. This max digit serves as the sort key in the sorted() function.
Method 2: Using a Lambda Function
A lambda function can serve as an inline key function, making the code more concise by eliminating the need for a separate function definition outside of the sorted() call.
Here’s an example:
numbers = [123, 45, 299, 38] sorted_numbers = sorted(numbers, key=lambda x: int(max(str(x)))) print(sorted_numbers)
Output: [123, 38, 45, 299]
The lambda function operates identically to the custom key function from Method 1, but it’s defined inline within the sorted() function call.
Method 3: Utilizing List Comprehension
List comprehension can be used to generate key-value pairs of the original numbers and their maximum digit, then sort based on these pairs.
Here’s an example:
numbers = [123, 45, 299, 38] sorted_numbers = [num for max_digit, num in sorted((int(max(str(num))), num) for num in numbers)] print(sorted_numbers)
Output: [123, 38, 45, 299]
This snippet creates tuples of the maximum digit and the original number, sorts the list of tuples, and then extracts the numbers into a new list in the sorted order.
Method 4: Using the Operator Module
The operator module provides a way to use the itemgetter() function to extract the sort key, which is particularly useful when working with lists of tuples.
Here’s an example:
from operator import itemgetter numbers = [123, 45, 299, 38] # Create a list of tuples with the max digit and original number pairs = [(int(max(str(num))), num) for num in numbers] # Sort tuples based on the max digit pairs.sort(key=itemgetter(0)) # Extract the numbers from the sorted tuples sorted_numbers = [num for _, num in pairs] print(sorted_numbers)
Output: [123, 38, 45, 299]
This code snippet first creates a list of tuples, sorts the list of tuples with itemgetter() serving as the key function, and finally constructs the sorted list of numbers by extracting the second item of each tuple.
Bonus One-Liner Method 5: Using Complex Number Sorting
Python’s ability to sort complex numbers based on the real part first and then the imaginary part can be exploited by treating the maximum digit as the real part.
Here’s an example:
numbers = [123, 45, 299, 38] sorted_numbers = sorted(numbers, key=lambda num: complex(int(max(str(num))), num)) sorted_numbers = [int(n.imag) for n in sorted_numbers] print(sorted_numbers)
Output: [123, 38, 45, 299]
This clever hack takes advantage of the sorting behavior for complex numbers in Python by attaching the maximum digit as the real part and the number itself as the imaginary part.
Summary/Discussion
- Method 1: Custom Key Function. Provides clear intention, easy to understand. Could be verbose for simple tasks.
- Method 2: Lambda Function. More concise, ideal for one-off sorting tasks. Less readable for users unfamiliar with lambda functions.
- Method 3: List Comprehension. More Pythonic and compact. Can be less intuitive for those not well-versed in list comprehensions.
- Method 4: Operator Module. Utilizes standard library tools, clean separation of tuple creation and sorting. Additional importing required, might be less straightforward than other methods.
- Method 5: Complex Number Sorting. One-liner, novel approach. Highly unconventional and could be confusing without proper comments explaining the logic.