Sorting Palindrome Words in a Sentence Using Python

💡 Problem Formulation: Imagine you have a sentence containing a mixture of words, and you want to extract and sort all the palindrome words within it. A palindrome word reads the same backward as forward, such as ‘radar’ or ‘level.’ Given an input sentence like “Anna went to see civic duty in a racecar,” the desired output would be a list of palindrome words sorted alphabetically: [‘Anna’, ‘civic’, ‘racecar’].

Method 1: Using Iteration and String Methods

This method involves iterating through each word in the sentence, checking if it is a palindrome using the string slicing technique, and then sorting the resulting list of palindromes. The algorithm is both intuitive and straightforward, making use of the inherently readable nature of Python code.

Here’s an example:

def sort_palindromes(sentence):
    words = sentence.split()
    palindromes = [word for word in words if word.lower() == word.lower()[::-1]]
    return sorted(palindromes)

print(sort_palindromes("Anna went to see civic duty in a racecar"))

Output:

['Anna', 'civic', 'racecar']

The code defines a function sort_palindromes() that splits the given sentence into words and then filters out the palindrome words using a list comprehension that checks if the word is equal to its reversal. Finally, the palindromes are sorted alphabetically.

Method 2: Using Regular Expressions

This method employs regular expressions to tokenize the sentence into words, subsequently checks each for palindromic properties, and sorts them. Regular expressions provide a powerful way to work with strings and can be especially useful when the input text requires more complex processing rules.

Here’s an example:

import re

def sort_palindromes(sentence):
    words = re.findall(r'\b\w+\b', sentence)
    palindromes = [word for word in words if word.lower() == word.lower()[::-1]]
    return sorted(palindromes)

print(sort_palindromes("Anna went to see civic duty in a racecar"))

Output:

['Anna', 'civic', 'racecar']

The function sort_palindromes() here first uses the regular expression re.findall() to extract all words from the sentence. After identifying palindromes through a list comprehension, the function sorts and returns them. This method is particularly good if the input string may contain complex word delimiters.

Method 3: Utilizing Filter and Lambda

This method makes use of Python’s built-in function filter() alongside a lambda function to extract palindromes from the sentence. The anonymous lambda function serves as a quick, concise way to define the logic for palindrome checking.

Here’s an example:

def sort_palindromes(sentence):
    words = sentence.split()
    is_palindrome = lambda word: word.lower() == word.lower()[::-1]
    palindromes = filter(is_palindrome, words)
    return sorted(palindromes)

print(sort_palindromes("Anna went to see civic duty in a racecar"))

Output:

['Anna', 'civic', 'racecar']

In this approach, sort_palindromes() defines a lambda function for checking palindromes and applies it with filter() to retain only palindrome words. The final list of sorted words is then returned. This method is elegant and can be more efficient for large datasets, as filter operations can be faster than list comprehensions for big lists.

Method 4: Using Python’s Built-in Functions map() and reversed()

Here, Python’s map function applies the reversed() function to transform each word in the sentence, simplifying the process of checking for palindromes and sorting them.

Here’s an example:

def sort_palindromes(sentence):
    words = sentence.split()
    palindromes = [word for word in words if word.lower() == ''.join(map(str.lower, reversed(word)))]
    return sorted(palindromes)

print(sort_palindromes("Anna went to see civic duty in a racecar"))

Output:

['Anna', 'civic', 'racecar']

This version of sort_palindromes() uses map() together with reversed() to check for palindromes. The rest of the function mirrors the previous examples, with a final sort of the palindromes identified. This method can be more readable to those familiar with map and reversed patterns in functional programming.

Bonus One-Liner Method 5: Using List Comprehension and Python’s Built-in Functions

This brief one-liner combines list comprehension and Python’s built-in functions for an efficient and compact solution.

Here’s an example:

print(sorted(word for word in "Anna went to see civic duty in a racecar".split() if word.lower() == word.lower()[::-1]))

Output:

['Anna', 'civic', 'racecar']

This one-liner demonstrates the elegance and expressiveness of Python. It sorts a list of words created from a string split, filtered by whether each word is a palindrome, all in a single line. While concise, this method offers less readability and can be harder to understand for those new to Python.

Summary/Discussion

• Method 1: Iteration and String Methods. Straightforward and easy to understand. May not handle complex delimiter cases well.
• Method 2: Regular Expressions. Excellent for complex text formats, but can be overkill for simple cases and is generally slower than direct string operations.
• Method 3: Filter and Lambda. Efficient for large data sets. Lambda functions may be less readable for beginners.
• Method 4: map() and reversed(). Good readability for those familiar with functional programming. The use of map may be unnecessary for simple cases.
• Bonus One-Liner Method 5: List Comprehension with Built-in Functions. Extremely concise but potentially less readable. Quick for small datasets but may not scale as well for larger data.