The counter is a container included in the collections module. Now you all must be wondering what is a container. Don’t worry first let’s discuss the container.
What is Container?
Containers are objects that hold objects. They provide a way to access the contained objects and iterate over them. Examples of built-in containers are Tuples, lists, and dictionaries. Others are included in the Collections module.
A Counter is a subclass of dict. Therefore it is an unordered collection where elements and their respective count are stored as a dictionary. This is equivalent to a bag or multiset of other languages.
Syntax
class collections.Counter([iterable-or-mapping])
Initialization:
The constructor of the counter can be called in any one of the following ways:
- With a sequence of items
- With a dictionary containing keys and counts
- With keyword arguments mapping string names to counts
Initializing a Counter
Python3
# A Python program to show different ways to create# Counterfrom collections import Counter# With sequence of itemsprint(Counter(['B','B','A','B','C','A','B','B','A','C']))# with dictionaryprint(Counter({'A':3, 'B':5, 'C':2}))# with keyword argumentsprint(Counter(A=3, B=5, C=2)) |
Output:
Counter({'B': 5, 'A': 3, 'C': 2})
Counter({'B': 5, 'A': 3, 'C': 2})
Counter({'B': 5, 'A': 3, 'C': 2})
Updation in counters
We can also create an empty counter in the following manner :
coun = collections.Counter()
And can be updated via the update() method. The syntax for the same :
coun.update(Data)
Python3
# A Python program to demonstrate update()from collections import Countercoun = Counter()coun.update([1, 2, 3, 1, 2, 1, 1, 2])print(coun)coun.update([1, 2, 4])print(coun) |
Output:
Counter({1: 4, 2: 3, 3: 1})
Counter({1: 5, 2: 4, 3: 1, 4: 1}
Subtract two Counters
Data can be provided in any of the three ways as mentioned in initialization and the counter’s data will be increased not replaced.Counts can be zero or negative also.
Python3
# Python program to demonstrate that counts in# Counter can be 0 and negativefrom collections import Counterc1 = Counter(A=4, B=3, C=10)c2 = Counter(A=10, B=3, C=4)c1.subtract(c2)print(c1) |
Output:
Counter({'c': 6, 'B': 0, 'A': -6})
Distinct Count in the list
We can use Counter to count distinct elements of a list or other collections.
Python3
# An example program where different list items are# counted using counterfrom collections import Counter# Create a listz = ['blue', 'red', 'blue', 'yellow', 'blue', 'red']# Count distinct elements and print Counter aobjectprint(Counter(z)) |
Output:
Counter({'blue': 3, 'red': 2, 'yellow': 1})
Printing Counter Values
We can also access all the keys and values of a counter using the keys(), values(), and items() methods. These methods return views of the keys, values, and key-value pairs in the counter, respectively.
Python3
from collections import Countermy_counter = Counter('abracadabra')print(my_counter.keys())print(my_counter.values())print(my_counter.items()) |
Output:
dict_keys(['a', 'b', 'r', 'c', 'd'])
dict_values([5, 2, 2, 1, 1])
dict_items([('a', 5), ('b', 2), ('r', 2), ('c', 1), ('d', 1)])
If you want to learn more about accessing counters in Python, the article (Accessing Counters) is a great resource.
