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Get Least Common Element in a List in Python

April 30, 2023 / List, Python / By

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,

Frequently Asked:

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.

Python List Methods

List MethodDescription
append(x)Add an item to the end of the list.
extend(iterable)Extend the list by appending all the items from the iterable.
insert(i, x)Insert an item at a given position i.
remove(x)Remove the first item from the list whose value is x.
pop([i])Remove the item at the given position in the list and return it.
index(x[, start[, end]])Return the first index at which a value occurs.
count(x)Return the number of times x appears in the list.
sort([key[, reverse]])Sort the items of the list in place.
reverse()Reverse the elements of the list in place.
clear()Remove all items from the list.
copy()Return a shallow copy of the list.

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