Counter Class Of Python Collections Module

Overview:

  • The Counter class of Collections Module in Python is the implementation of the mathematical concept Multiset.

 

  • Unlike a Set, the Multiset can have the same elements several times (n), which is called the multiplicity of the element.

 

  • In short, a set has its elements and its multiplicity. A Multiset of (a, b, b, c, c, c) can be represented as a-1, b-2, c-3.

 

  • The final mapping in the above representation is nothing but a dictionary, which stores a set of key-value pairs.

 

  • Rephrasing the definition of the Counter class, a counter class in Python is a Multiset, which is implemented as a specialization of the python dictionary class dict.

 

  • Like the way a Python dictionary stores name value pairs, a Counter object in Python stores the elements of a Multiset and their multiplicities.

 

  • All of the following operations result in the replacement of the latest count corresponding to the element specified.

 

  • Creation of the counter by specifying an element and its counter multiple times.
    • c = Collections.counter{“a”:10, “a”:12, “a”:14}

will make the count of “a” as 14.

 

  • Set the count using the element
    • c[“a”] = 55 – will make the count of ‘a’ as 55

 

  • Calling update() method on a counter object in Python increases the counter of an element by the value specified.

Example1:

import collections

 

# Create a counter

colorCount = collections.Counter({"red","blue","green"})

print("Counter Object:")

print(colorCount)

 

# Replace the count of red by 2

colorCount["red"] = 2

print("Counter Object after replacing the red count by 2:")

print(colorCount)

 

Output:

Counter Object:

Counter({'green': 1, 'red': 1, 'blue': 1})

Counter Object after replacing the red count by 2:

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

 

Example2:

import collections

 

# Create a counter

colorCount = collections.Counter({"red":"5","blue":"6","green":"7"})

print("Counter Object:")

print(colorCount)

 

# Replace the count of green by 9

colorCount["green"] = 9

print("Counter Object after replacing the green count by 9:")

print(colorCount)

 

 

# Increase the green count by 2

colorCount.update({"green":2})

print("Counter Object after increasing the green count by 2:")

print(colorCount)

 

# Decrease the green count by 1

colorCount.update({"green":-1})

print("Counter Object after decreasing the green count by 1:")

print(colorCount)

 

Output:

Counter Object:

Counter({'green': '7', 'blue': '6', 'red': '5'})

Counter Object after replacing the green count by 9:

Counter({'red': '5', 'blue': '6', 'green': 9})

Counter Object after increasing the green count by 2:

Counter({'red': '5', 'blue': '6', 'green': 11})

Counter Object after decreasing the green count by 1:

Counter({'red': '5', 'blue': '6', 'green': 10})

 


Copyright 2018 © pythontic.com