Counter in Python : A dictionary subclass of elements and their counts Declaring adding searching and removing elements

Counter is a subclass of dictionary with keys as elements and their counts as values.

from collections import Counter
my_list=['One','Two','One','Three']
my_counter=Counter(my_list) 
print(my_counter)    # Counter({'One': 2, 'Two': 1, 'Three': 1})

We can read any values

print(my_counter['Two']) # 1

Using a string

from collections import Counter
my_str='Hello'
my_counter=Counter(my_str)
print(my_counter)  # Counter({'l': 2, 'H': 1, 'e': 1, 'o': 1})

Using a list

from collections import Counter
my_list=[1,3,4,2,3,2]
my_counter=Counter(my_list)
print(my_counter)         # Counter({3: 2, 2: 2, 1: 1, 4: 1})

Getting type() of counter

from collections import Counter
my_list=[1,3,4,2,3,2]
my_counter=Counter(my_list)
print(type(my_counter)) # <class 'collections.Counter'>

Using items(), keys(), values()

We can use all these methods, here are sample scripts.

from collections import Counter
my_list=[1,3,4,2,3,2]
my_counter=Counter(my_list)
for k,v in my_counter.items():
  print("Keys:",k,", Values:", v)

Output

Keys: 1 , Values: 1
Keys: 3 , Values: 2
Keys: 4 , Values: 1
Keys: 2 , Values: 2

Using keys()

from collections import Counter
my_list=[1,3,4,2,3,2]
my_counter=Counter(my_list)
for k in my_counter.keys():
  print("Keys:",k)

Output

Keys: 1
Keys: 3
Keys: 4
Keys: 2

Using values()

from collections import Counter
my_list=[1,3,4,2,3,2]
my_counter=Counter(my_list)
for v in my_counter.values():
  print("Values :",v)

Output

Values : 1
Values : 2
Values : 1
Values : 2

Getting the Key and value of element with Maximum value.

from collections import Counter
my_list=[1,3,4,2,3,2,3,1,3]
my_counter=Counter(my_list)
key_of_max_value = max(my_counter, key=my_counter.get) 
print(key_of_max_value,my_counter[key_of_max_value])

Output

3 4

elements()

By using elements() method we can get the original list.

from collections import Counter
my_list=[1,3,4,2,3,2]
my_counter=Counter(my_list)
print(my_counter)                  # Counter({3: 2, 2: 2, 1: 1, 4: 1})
print(list(my_counter.elements())) # [1, 3, 3, 4, 2, 2]

most_common()

most_common(n) returns frequently used elements as keys and counts as values. The optional parameter n can be used to restrict the number of elements to return.

from collections import Counter
my_list=[1,3,4,2,3,2]
my_counter=Counter(my_list)
print(my_counter.most_common())  #  [(3, 2), (2, 2), (1, 1), (4, 1)]

from collections import Counter
my_list=[1,3,4,2,3,2]
my_counter=Counter(my_list)
my_common=my_counter.most_common()
for no,count in my_common:
  #print("elements =   %d: %d" % (no, count))
  print("Element = {}: Occurrences {}".format(no, count))

Getting 2 elements only.

from collections import Counter
my_list=[1,3,4,2,3,2]
my_counter=Counter(my_list)
my_common=my_counter.most_common(2)
for no,count in my_common:
    print("Element = {}: Occurrences {}".format(no, count))

Output

Element = 3: Occurrences 2
Element = 2: Occurrences 2

update()

Counter is not immutable , so we can add elements

from collections import Counter
my_list=[1,3,4,2,3,2]
my_counter=Counter(my_list)
my_counter.update([8,9])  # add two more elements 
print(my_counter)  # Counter({3: 2, 2: 2, 1: 1, 4: 1, 8: 1, 9: 1})

We can add existing elements

from collections import Counter
my_list=[1,3,4,2,3,2]
my_counter=Counter(my_list)
my_counter.update([3,1])  # add two more elements 
print(my_counter)  # Counter({3: 3, 1: 2, 2: 2, 4: 1})

We can initialize counter and then add elements.

from collections import Counter
my_counter=Counter()
my_list=[1,3,3,2]
my_counter.update(my_list)
print(my_counter)  # Counter({3: 2, 1: 1, 2: 1})

clear()

Clear the Counter.

from collections import Counter
my_list=[1,3,3,2]
my_counter=Counter(my_list)
print(my_counter)   #   Counter({3: 2, 1: 1, 2: 1})
print(my_counter.clear()) # None

Counter Arithmetic

Add, subtract, and, or

from collections import Counter
my_list1=Counter([1,3,3,2])
my_list2=Counter([3,4,5,2])
print(my_list1 + my_list2) # Counter({3: 3, 2: 2, 1: 1, 4: 1, 5: 1})
print(my_list1 - my_list2) # Counter({1: 1, 3: 1})
print(my_list1 & my_list2) # Counter({3: 1, 2: 1})
print(my_list1 | my_list2) # Counter({3: 2, 1: 1, 2: 1, 4: 1, 5: 1})

Using string and split() we created list and then counter.

from collections import Counter
my_str1='Welcome to plus2net'
my_str2='Welcome to Python'
my_counter1=Counter(my_str1.split(' '))
my_counter2=Counter(my_str2.split(' '))
print(my_counter1 - my_counter2)
print(my_counter1 + my_counter2)
print(my_counter1 & my_counter2)
print(my_counter1 | my_counter2)

Output

Counter({'plus2net': 1})
Counter({'Welcome': 2, 'to': 2, 'plus2net': 1, 'Python': 1})
Counter({'Welcome': 1, 'to': 1})
Counter({'Welcome': 1, 'to': 1, 'plus2net': 1, 'Python': 1})

We will get the common words used in two strings by using & operation.

print(my_counter1 & my_counter2)

All String methods tuple Python- Tutorials

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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Counter(): for counting hashable objects

Using items(), keys(), values()

elements()

most_common()

update()

clear()

Counter Arithmetic

Subhendu Mohapatra