How to Count Frequency Using Counter in Python

Use Counter from Python's collections module to count the frequency of items in a list or string. Simply pass your data to Counter(), and it returns a dictionary-like object with items as keys and their counts as values.

Syntax

The basic syntax to use Counter is:

• from collections import Counter - imports the Counter class.
• Counter(iterable) - creates a Counter object counting elements in the iterable (like a list or string).
• The result is a dictionary-like object where keys are items and values are their counts.

python

from collections import Counter

counter = Counter(iterable)

Example

This example shows how to count the frequency of letters in a string and numbers in a list using Counter.

python

from collections import Counter

# Count frequency of letters in a string
text = 'hello world'
letter_counts = Counter(text)
print('Letter counts:', letter_counts)

# Count frequency of numbers in a list
numbers = [1, 2, 2, 3, 3, 3, 4]
number_counts = Counter(numbers)
print('Number counts:', number_counts)

Output

Letter counts: Counter({'l': 3, 'o': 2, 'h': 1, 'e': 1, ' ': 1, 'w': 1, 'r': 1, 'd': 1})
Number counts: Counter({3: 3, 2: 2, 1: 1, 4: 1})

Common Pitfalls

Common mistakes when using Counter include:

• Passing a non-iterable object, which causes an error.
• Expecting Counter to sort results automatically; it does not sort by count.
• Modifying the Counter object incorrectly instead of using its methods.

Always ensure your input is iterable and use most_common() to get sorted counts.

python

from collections import Counter

# Wrong: passing an integer (not iterable)
# counter = Counter(123)  # This raises TypeError

# Right: pass a string or list
counter = Counter('123')
print(counter)

# To get sorted counts by frequency
counter = Counter(['apple', 'banana', 'apple', 'orange', 'banana', 'apple'])
print(counter.most_common())

Output

Counter({'1': 1, '2': 1, '3': 1})
[('apple', 3), ('banana', 2), ('orange', 1)]

Quick Reference

Here is a quick summary of useful Counter methods:

Method	Description
Counter(iterable)	Create a Counter object counting elements in iterable
most_common(n)	Return a list of the n most common elements and their counts
elements()	Return an iterator over elements repeating each as many times as its count
update(iterable)	Add counts from another iterable or mapping
subtract(iterable)	Subtract counts using another iterable or mapping

Key Takeaways

Use collections.Counter to count frequency of items in any iterable easily.

Pass a list, string, or other iterable to Counter to get counts as a dictionary-like object.

Use most_common() to get items sorted by frequency.

Ensure input is iterable to avoid errors.

Counter provides helpful methods to update, subtract, and iterate over counts.