How to Efficiently Count Word Occurrences in a Python List?

Item Frequency Count in Python

How do you efficiently count the occurrences of each unique word in a given list? Consider the following code:

<code class="python">words = "apple banana apple strawberry banana lemon"
uniques = set(words.split())
freqs = [(item, words.split().count(item)) for item in uniques]
print(freqs)</code>

While this method works, it requires two iterations through the list, once to create the unique word set and again to count appearances. Can we optimize this?

Solution: Using the Counter Class

The Python collections module provides a Counter class specifically designed for this task. Here's how you can use it:

<code class="python">from collections import Counter
words = "apple banana apple strawberry banana lemon"
Counter(words.split())
# Output: Counter({'apple': 2, 'banana': 2, 'strawberry': 1, 'lemon': 1})</code>

The Counter class counts the occurrences of each item in the provided iterable, resulting in a dictionary where keys are unique items and values are their counts. This approach is more efficient as it only requires a single iteration through the input list.

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