Python Counter - Python Collections Counter

Published on August 3, 2022


Python Counter - Python Collections Counter

While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the “report an issue“ button at the bottom of the tutorial.

Python Counter class is part of Collections module. Counter is a subclass of Dictionary and used to keep track of elements and their count.

Python Counter

Counter is an unordered collection where elements are stored as Dict keys and their count as dict value. Counter elements count can be positive, zero or negative integers. However there is no restriction on it’s keys and values. Although values are intended to be numbers but we can store other objects too.

Creating Python Counter Object

We can create an empty Counter or start with some initial values too.

from collections import Counter

# empty Counter
counter = Counter()
print(counter)  # Counter()

# Counter with initial values
counter = Counter(['a', 'a', 'b'])
print(counter)  # Counter({'a': 2, 'b': 1})

counter = Counter(a=2, b=3, c=1)
print(counter)  # Counter({'b': 3, 'a': 2, 'c': 1})

We can also use any Iterable as argument for creating Counter object. So string literal and List can be used too for creating Counter object.

# Iterable as argument for Counter
counter = Counter('abc')
print(counter)  # Counter({'a': 1, 'b': 1, 'c': 1})

# List as argument to Counter
words_list = ['Cat', 'Dog', 'Horse', 'Dog']
counter = Counter(words_list)
print(counter)  # Counter({'Dog': 2, 'Cat': 1, 'Horse': 1})

# Dictionary as argument to Counter
word_count_dict = {'Dog': 2, 'Cat': 1, 'Horse': 1}
counter = Counter(word_count_dict)
print(counter)  # Counter({'Dog': 2, 'Cat': 1, 'Horse': 1})

As I mentioned above, we can use non-numeric data for count values too, but that will defect the purpose of Counter class.

# Counter works with non-numbers too
special_counter = Counter(name='Pankaj', age=20)
print(special_counter)  # Counter({'name': 'Pankaj', 'age': 20})

Python Counter Methods

Let’s look into Counter class methods and some other operations we can perform on it.

Getting Count of Elements

# getting count
counter = Counter({'Dog': 2, 'Cat': 1, 'Horse': 1})
countDog = counter['Dog']
print(countDog)  # 2

If we try to get the count of non-existing key, it will return 0 and not throw KeyError.

# getting count for non existing key, don't cause KeyError
print(counter['Unicorn'])  # 0

Setting Count of Elements

We can also set the count of existing element in the counter. If the element doesn’t exist, then it gets added to the counter.

counter = Counter({'Dog': 2, 'Cat': 1, 'Horse': 1})
# setting count
counter['Horse'] = 0
print(counter)  # Counter({'Dog': 2, 'Cat': 1, 'Horse': 0})

# setting count for non-existing key, adds to Counter
counter['Unicorn'] = 1
print(counter)  # Counter({'Dog': 2, 'Cat': 1, 'Unicorn': 1, 'Horse': 0})

Deleting an element from Counter

We can use del to delete an element from the counter object.

# Delete element from Counter
del counter['Unicorn']
print(counter)  # Counter({'Dog': 2, 'Cat': 1, 'Horse': 0})


This method returns the list of elements in the counter. Only elements with positive counts are returned.

counter = Counter({'Dog': 2, 'Cat': -1, 'Horse': 0})

# elements()
elements = counter.elements()  # doesn't return elements with count 0 or less
for value in elements:

Above code will print “Dog” two times because it’s count is 2. Other elements will be ignored because they don’t have positive count. Counter is an unordered collection, so elements are returned in no particular order.


This method returns the most common elements from the counter. If we don’t provide value of ‘n’ then sorted dictionary is returned from most common the least common elements. We can use slicing to get the least common elements on this sorted dictionary.

counter = Counter({'Dog': 2, 'Cat': -1, 'Horse': 0})

# most_common()
most_common_element = counter.most_common(1)
print(most_common_element)  # [('Dog', 2)]

least_common_element = counter.most_common()[:-2:-1]
print(least_common_element)  # [('Cat', -1)]

subtract() and update()

Counter subtract() method is used to subtract element counts from another counter. update() method is used to add counts from another counter.

counter = Counter('ababab')
print(counter)  # Counter({'a': 3, 'b': 3})
c = Counter('abc')
print(c)  # Counter({'a': 1, 'b': 1, 'c': 1})

# subtract
print(counter)  # Counter({'a': 2, 'b': 2, 'c': -1})

# update
print(counter)  # Counter({'a': 3, 'b': 3, 'c': 0})

Python Counter Arithmetic Operations

We can perform some arithmetic operations on Counters too, just like numbers. However only elements with positive count are returned with these operations.

# arithmetic operations
c1 = Counter(a=2, b=0, c=-1)
c2 = Counter(a=1, b=-1, c=2)

c = c1 + c2  # return items having +ve count only
print(c)  # Counter({'a': 3, 'c': 1})

c = c1 - c2  # keeps only +ve count elements
print(c)  # Counter({'a': 1, 'b': 1})

c = c1 & c2  # intersection min(c1[x], c2[x])
print(c)  # Counter({'a': 1})

c = c1 | c2  # union max(c1[x], c2[x])
print(c)  # Counter({'a': 2, 'c': 2})

Miscellaneous Operations on Python Counter

Let’s look at some code snippets for miscellaneous operations we can perform on Counter objects.

counter = Counter({'a': 3, 'b': 3, 'c': 0})
# miscellaneous examples
print(sum(counter.values()))  # 6

print(list(counter))  # ['a', 'b', 'c']
print(set(counter))  # {'a', 'b', 'c'}
print(dict(counter))  # {'a': 3, 'b': 3, 'c': 0}
print(counter.items())  # dict_items([('a', 3), ('b', 3), ('c', 0)])

# remove 0 or negative count elements
counter = Counter(a=2, b=3, c=-1, d=0)
counter = +counter
print(counter)  # Counter({'b': 3, 'a': 2})

# clear all elements
print(counter)  # Counter()

That’s all for Python Counter class.

You can download the complete example code from my GitHub Repository.

Reference: Python Docs

Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.

Learn more about our products

About the authors
Default avatar


Still looking for an answer?

Ask a questionSearch for more help

Was this helpful?
DigitalOcean Employee
DigitalOcean Employee badge
May 17, 2021

Hi Pankaj, You have prepared the notes very nicely and precisely. Keep it up. Thank you.

- Amit Hiremath

    DigitalOcean Employee
    DigitalOcean Employee badge
    January 22, 2021

    The output of the update method is actually: Counter({‘a’: 4, ‘b’: 4, ‘c’: 1})

    - Danilo Burbano

      DigitalOcean Employee
      DigitalOcean Employee badge
      April 27, 2020

      what is the return type of a collection.counter?

      - Shikha Kumawat

        DigitalOcean Employee
        DigitalOcean Employee badge
        December 17, 2019

        how can i write python program to get this output by using counter 1 2 (1,2) 3 4 (3,4) Note : this is a list and should the user input the length of the list and the element and the program after two index should take the previous two number and put them in a group .

        - RK

          DigitalOcean Employee
          DigitalOcean Employee badge
          July 28, 2019

          How to get index of counter element Like : a=[“a”,“a”,“b”,“c”,“d”,“d”,“d”] I want to know where a=2,d=3

          - Alok

            Try DigitalOcean for free

            Click below to sign up and get $200 of credit to try our products over 60 days!

            Sign up

            Join the Tech Talk
            Success! Thank you! Please check your email for further details.

            Please complete your information!

            Featured on Community

            Get our biweekly newsletter

            Sign up for Infrastructure as a Newsletter.

            Hollie's Hub for Good

            Working on improving health and education, reducing inequality, and spurring economic growth? We'd like to help.

            Become a contributor

            Get paid to write technical tutorials and select a tech-focused charity to receive a matching donation.

            Welcome to the developer cloud

            DigitalOcean makes it simple to launch in the cloud and scale up as you grow — whether you're running one virtual machine or ten thousand.

            Learn more
            DigitalOcean Cloud Control Panel