Python Count Occurrences in list

Glance about ‘List’

A list is a collection of items, which can be of different data types, including numbers, strings, and other objects in python. Lists are defined using square brackets ‘[]‘ and items are separated by commas. Lists are mutable, meaning the elements within the list can be changed.

Example:

a = [1, 2, 3, 4, 5]
b = ["apple", "banana", "cherry"]
c = [1, "apple", 3.14, True]

To count how many times an item appears on a list

In Python, you can use the ‘list.count()‘ method to count the number of times an item appears in a list.

Example:

a = [1, 2, 3, 1, 2, 3, 4, 5, 6, 1]
count = a.count(1)
print(count) 

Output:

3

You can also use a for loop and an if statement to check each element in the list and increment a counter for each match.

Example:

a = [1, 2, 3, 1, 2, 3, 4, 5, 6, 1]
count = 0
for i in a:
    if i == 1:
        count += 1
print(count) 

Output:

3

Repeat items in a list

You can repeat items in a list in Python using the multiplication operator ‘*‘ or list comprehension.

To repeat an item using the multiplication operator, you simply multiply the item by an integer. Here’s an example:

my_list = ['apple'] * 3
print(my_list)  

Output:

'apple', 'apple', 'apple'

In this example, we have a list ‘my_list‘ containing a single string 'apple'. We use the multiplication operator ‘*‘ to repeat the string three times, resulting in a new list with three strings.

You can also use list comprehension to repeat an item. Here’s an example:

my_list = ['apple' for _ in range(3)]
print(my_list)  

Output:

'apple', 'apple', 'apple'

In this example, we use list comprehension to create a new list with three strings 'apple'. The ‘for‘ loop in the list comprehension iterates three times, creating a new string 'apple' on each iteration.

Both of these methods can be used to repeat any item in a list, not just strings. For example, you could repeat numbers, boolean values, or even other lists.