Counters in Python | Set 1 (Initialization and Updation)

What is counter?
Counter is a container included in the collections module.

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 Tuple, list and dictionary. Others are included in Collections module.

A Counter is a subclass of dict. Therefore it is an unordered collection where elements and their respective count are stored as dictionary. This is equivalent to bag or multiset of other languages.

Syntax :
class collections.Counter([iterable-or-mapping])

Initialization :
The constructor of counter can be called in any one of the following ways :

Example of each type of initialization :

Output of all the three lines is same :

Counter({'B': 5, 'A': 3, 'C': 2})
Counter({'B': 5, 'A': 3, 'C': 2})
Counter({'B': 5, 'A': 3, 'C': 2})

Updation :
We can also create an empty counter in the following manner :

coun = collections.Counter()

And can be updated via update() method .Syntax for the same :

coun.update(Data)

Output :

Counter({1: 4, 2: 3, 3: 1})
Counter({1: 5, 2: 4, 3: 1, 4: 1})

• 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 and negative also.
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  # Python program to demonstrate that counts in  # Counter can be 0 and negative from collections import Counter    c1 = Counter(A=4,  B=3, C=10) c2 = Counter(A=10, B=3, C=4)    c1.subtract(c2) print(c1)

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  Output :

   Counter({'c': 6, 'B': 0, 'A': -6})

• We can use Counter to count distinct elements of a list or other collections.
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  # An example program where different list items are # counted using counter from collections import Counter    # Create a list z = ['blue', 'red', 'blue', 'yellow', 'blue', 'red']    # Count distinct elements and print Counter aboject print(Counter(z))

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  Output:

  Counter({'blue': 3, 'red': 2, 'yellow': 1})
  

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