Python | Create list of numbers with given range

Given two numbers r1 and r2 (which defines the range), write a Python program to create a list with the given range (inclusive). 

Examples:

Input : r1 = -1, r2 = 1
Output : [-1, 0, 1]

Input : r1 = 5, r2 = 9
Output : [5, 6, 7, 8, 9]

Let’s discuss a few approaches to Creating a list of numbers with a given range in Python. 

Naive Approach using a loop

A naive method to create a list within a given range is to first create an empty list and append the successor of each integer in every iteration of for loop. 

Output:

[-1, 0, 1]

Using List comprehension 

We can also use list comprehension for the purpose. Just iterate ‘item’ in a for loop from r1 to r2 and return all ‘item’ as list. This will be a simple one liner code. 

Output:

[-1, 0, 1]

Using Python range()

Python comes with a direct function range() which creates a sequence of numbers from start to stop values and print each item in the sequence. We use range() with r1 and r2 and then convert the sequence into list. 

Output:

[-1, 0, 1]

Using itertools:

You can also use the range function in combination with the itertools module’s chain function to create a list of numbers with a given range. This can be done as follows:

[-5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5]

This will create a list of numbers from r1 to r2 inclusive by chaining the elements in the range together using the chain function from the itertools module.

Using numpy.arange() 

Python numpy.arange() returns a list with evenly spaced elements as per the interval. Here we set the interval as 1 according to our need to get the desired output. 

Output:

[-1, 0, 1]

Using numpy to create list of numbers with given range

Here we are creating a list of numbers from a given range with the defined increment.

Output:

[1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0]

Using Recursion

Another approach to create a list of numbers within a given range is to use recursion. This involves defining a recursive function that takes in the current range and the list to be returned, and then appending the current range to the list and calling the function again with the next range until the end of the range is reached.

[5, 6, 7, 8, 9]
[-1, 0, 1]

This approach has a time complexity of O(n) and an auxiliary space of O(n), where n is the number of elements in the list.

Approach 5: Using map() and lambda function

In this approach, we use map() and a lambda function to generate a list of numbers within the given range. map() applies the lambda function to each element in the sequence and returns a map object. We convert the map object to a list and return it.

Algorithm

Use map() and a lambda function to generate a list of numbers within the given range.
Convert the map object to a list and return it.

[5, 6, 7, 8, 9]
[-1, 0, 1]

Time Complexity: O(r2-r1) where r1 and r2 are the given range.
Space Complexity: O(r2-r1) where r1 and r2 are the given range.