Counters in Python | Set 1 (initialization and update)

What is a container?
Containers — these are objects that contain objects. They provide a way to access and iterate over contained objects. Examples of built-in containers are Tuple, List, and Dictionary. Others are included in the Collections module.

Counter — it is a subclass of dict. Hence, it is an unordered collection in which the elements and their corresponding values ​​are stored as a dictionary. This is equivalent to a bag or a multitude of other languages.

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

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

With a sequence of items

With a dictionary containing keys and numbers

With keyword arguments mapping line names to counters

An example of each type of initialization:

# Python program to show different ways creation # Counter from collections import Counter   # With a sequence of items print Counter ([ ’B’ , ’B’ , ’ A’ , ’B’ , ’ C’ , ’A’ , ’ B’ , ’B’ , ’A’ , ’ C’ ])   # with dictionary print Counter ({ ’A’ : 3 , ’B’ : < / code> 5 , ’C’ : 2 })    # with keyword arguments print Counter (A = 3 , B = 5 , C = 2 )

The output of all three lines is the same:

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

Update:
We can also create an empty counter like this:

 coun = collections.Counter () 

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

 coun.update (Data) 

# Python program to demonstrate update () from collections import Counter coun = 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}) 

• Data can be provided in any of three ways, as indicated in the initialization, and the counter data will be incremented, not replaced.
• The score can be either zero or negative.

  # Python program to demonstrate what counts < br /> # Counter can be 0 or 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)

  Exit:

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

• We can use Counter to count individual list items or other collections.

  # An example program where different elements of the list # counted using counter from collections import Counter   # Create list z = [ ’ blue’ , ’red’ , ’blue’ , ’ yellow’ , ’blue’ , ’ red’ ]   # Count individual items and print counter print (Counter (z))

  Output:

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

This article is updated by Mayank Rawat If you love Python.Engineering and would like to contribute, you can also write article using contribute.python.engineering or by mailing article [email protected] See my article appearing on the Python.Engineering homepage and help other geeks.

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