How to Count the frequencies in a list using a dictionary in Python?

A dictionary can be used to count the frequencies of elements in the list. Python example we will discuss how to count the frequencies in a list using a dictionary in Python.

Some of the topics which will be helpful for understanding the program implementation better are:

• List in Python
• Function in Python
• Dictionary in Python

1. Counting Frequencies Using a Dictionary

The keys in a dictionary must be unique, while values can be duplicated. We can use this property to count the frequencies of elements in a list by treating each element in the list as a key in a dictionary and incrementing its value for each occurrence.

Now let’s implement a program to count the frequencies of the elements in Python.

fruits = ['apple', 'banana', 'apple', 'orange', 'banana', 'banana', 'kiwi', 'apple']
fruit_freq = {}

for fruit in fruits:
  if fruit in fruit_freq:
    fruit_freq[fruit] += 1
  else:
    fruit_freq[fruit] = 1

print(fruit_freq)

Output
{'apple': 3, 'banana': 3, 'orange': 1, 'kiwi': 1}

For each fruit, we check if it is already a key in fruit_freq. If it is, we increment its value by 1 otherwise we add it to fruit_freq with a value of 1. Finally, we print fruit_freq to verify that the frequencies have been counted correctly.

2. Using the collections Module

The collections module in Python provides a built-in Counter class that can be used to count the frequencies of elements in a list. The Counter object automatically counts the frequencies of each element in the list.

Here’s an example:

from collections import Counter

fruits = ['apple', 'banana', 'apple', 'orange', 'banana', 'banana', 'kiwi', 'apple']
fruit_freq = Counter(fruits)

print(fruit_freq)

Output
Counter({'apple': 3, 'banana': 3, 'orange': 1, 'kiwi': 1})

3. Conclusion

In this Python example, we discussed multiple ways to count the frequencies in a list using a dictionary, one with a custom implementation and another using the Counter class.

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