Get Least Common Element in a List in Python

In this article, we will discuss different ways to get the least common element in a Python List.

Table Of Contents

Get Least Common Value in List

Import Counter class from collections module. The Counter class is a Dictionay subclass, and it is used for counting hashable items. Inside a Counter object, elements are stored as dictionary keys and their counts are stored as dictionary values. We can pass the list object to Counter() function, to get a Counter object. It will have all the unique elements of list as keys, and thier occurrence count as values.

Then call the most_common(n) function of Counter. It returns a list of the n most common elements and their counts from the Counter object. If n is not provided, then it returns all the unique elements in list, and their occurrence count in a decreading order of occurrence count. The last value in this list is the least common value, and its occurrence count. Let’s see an example,

from collections import Counter

listOfNums = [11, 15, 12, 11, 15, 16, 12, 11, 19, 15, 19, 16, 11, 12, 16, 12, 15]

# Get least common value, and its occurrence count
leastCommonValue , frequency = Counter(listOfNums).most_common()[-1]

print('Least Common Value : ', leastCommonValue)
print('Occurrence Count of Least Common Value : ', frequency)

Output:

Least Common Value :  19
Occurrence Count of Least Common Value :  2

The last common element in list was 19, with occurrence

Get N Least Common Values in List

To get the N least common values from a list, we need to pass the select the last N elements from list returned by most_common(). Let’s see an example,

from collections import Counter

listOfNums = [11, 15, 12, 11, 15, 16, 12, 11, 19, 15, 19, 16, 11, 12, 16, 12, 15]

# Get two least common values in list
values = Counter(listOfNums).most_common()[-2 : ]

for (value , frequency )in values:
    print('Value : ', value, ' :: Occurrence Count : ', frequency) 

Output:

Value :  16  :: Occurrence Count :  3
Value :  19  :: Occurrence Count :  2

We printed the two least common elements of list, along with thier occurrence count.

Summary

We learned how to get the least common value in a list in Python.