3 ways in Python to find the middle n list elements

Python program to find the middle n elements of a list:

In this post, we will learn how to find and print the middle n elements of a list in Python. The program will use a predefined list and take the value of n from the user.

We will also learn how to take the list numbers as inputs from the user to find the middle n elements. I will show you different ways to solve this problem.

Algorithm:

Let’s consider the following list:

[1, 2, 3, 4, 5, 6, 7, 8]

The middle 4 elements of this list are 3, 4, 5, and 6. To find these elements, we have to find the start and end indices of the list. We can use the following steps to find the start and the end indices:

Suppose n is the number of middle elements we want to find.
Find the length of the list. Divide this by 2.
Divide the n value by 2.
Subtract the value of step 3 from the value of step 2 to get the start index of the middle elements sublist.
Extract n elements from the start index to get the required middle elements.

We can use list slicing or iterate over the indices to pick the middle elements.

Example 1: Python program to find the middle n elements of a list by using a loop:

In this example, the program will use a for loop to iterate over the indices to find the mid n elements of the list.

given_list = [1, 2, 3, 4, 5, 6, 7, 8, 9]
n = 3

list_len = len(given_list)
start = list_len//2 - n//2

result_list = []

for i in range(start, start+n):
    result_list.append(given_list[i])

print(f'Given list: {given_list}')
print(f'Middle {n} elements of the list: {result_list}')

Here,

given_list is the given list of numbers.
The variable n represents the number of middle elements to find.
It uses the len() method to find the length of the list and assigns it to the list_len variable.
The starting index of the middle element list is assigned to the variable start.
It uses a for loop to find the n elements starting from the start index. The result elements are appended to the list result_list.
The last two lines are printing the given list and the result list.

If you run this program, it will print the below output:

Given list: [1, 2, 3, 4, 5, 6, 7, 8, 9]
Middle 3 elements of the list: [4, 5, 6]

Example 2: Python program to find the middle n elements of a list by using list slicing:

We can also use list slicing to find the middle n elements of a list. If we want to get the elements between indices start and end, we can use the below list slicing syntax:

list[start:end+1]

It will be similar to the above example. It will find the starting index of the middle element list and with list slicing, we can find the n elements starting from that index.

given_list = [1, 2, 3, 4, 5, 6, 7, 8]
n = 4

list_len = len(given_list)
start = list_len//2 - n//2

result_list = given_list[start:start+n]

print(f'Given list: {given_list}')
print(f'Middle {n} elements of the list: {result_list}')

This is similar to the above example. But instead of a for loop, we are using list slicing to find the middle elements.

If you run this program, it will print the below output:

Given list: [1, 2, 3, 4, 5, 6, 7, 8]
Middle 4 elements of the list: [3, 4, 5, 6]

Example 3: By using user input values:

The following example uses user input values to create the list. It also reads the value of n as input.

given_list = []

list_len = int(input("Enter the length of the list: "))
for i in range(list_len):
    given_list.append(int(input(f'Enter the number for index {i}: ')))

n = int(input("Enter the value of n: "))

list_len = len(given_list)
start = list_len//2 - n//2

result_list = given_list[start:start+n]

print(f'Given list: {given_list}')
print(f'Middle {n} elements of the list: {result_list}')

In this example, it reads the list values as inputs from the user and creates the list.

The list_len variable is used to hold the length of the list.
By using a for loop, it reads the numbers as inputs from the user.
It also reads the value of n from the user.

It will give output as below:

Enter the length of the list: 5
Enter the number for index 0: 1
Enter the number for index 1: 2
Enter the number for index 2: 3
Enter the number for index 3: 4
Enter the number for index 4: 5
Enter the value of n: 3
Given list: [1, 2, 3, 4, 5]
Middle 3 elements of the list: [2, 3, 4]

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