Python - Numbers in a list within a given range

We are given a list and we are given a range we need to count how many number lies in the given range. For example, we are having a list n = [5, 15, 25, 35, 45, 55, 65, 75] and we are having range lower=20, upper=60 so we need to count how many element lies between this range so that the output should be 4 in this case.

Using List Comprehension

List comprehension is one of the most efficient ways to solve this problem. It allows us to create a new list by filtering out the numbers that don’t fall within the specified range.

n = [5, 15, 25, 35, 45, 55, 65, 75]
l = 20
u = 60

# Count numbers in range using list comprehension
cnt = len([i for i in n if l <= i <= u])

print(cnt)

4

Explanation:

• List comprehension iterates through the list n and checks if each element i is within the specified range (l <= i <= u).
• len() function then counts how many elements satisfy the condition, returning the total count of numbers within the range

Other methods that we can use to count how many numbers in a list fall within a specific range are:

Using filter() and len()

filter() function is built into Python and allows us to filter a list based on a condition. It returns only the elements that satisfy the condition. After filtering the numbers that fall within the range we use len() function to count how many numbers are left.

n = [5, 15, 25, 35, 45, 55, 65, 75]
l = 20
u = 60

# Using filter and len
c = len(list(filter(lambda num: l <= n <= u, n)))

print(c)  

4

Explanation:

• filter() function filters elements in the numbers list based on the condition lower <= num <= upper, keeping only the numbers within the specified range.
• len() function counts number of filtered elements and returns the total count of numbers that fall within range.

Using sum() with a Generator Expression

This method uses sum() function which normally adds up numbers.

n = [5, 15, 25, 35, 45, 55, 65, 75]
l = 20
u = 60
# Using sum with generator expression
c = sum(1 for num in n if l <= n <= u)

print(c)  

4

Explanation:

• Generator expression iterates over each number in n and checks if it falls within the range [l, u].
• For each number that meets condition 1 is yielded and sum() adds these ones to count total numbers in range

Using for Loop

Using a simple for loop is the most straightforward and easy-to-understand method. We loop through each number in the list check if it is within range and increase the count if it is.

n = [5, 15, 25, 35, 45, 55, 65, 75]
l = 20
u = 60

# Simple loop method
c = 0
for num in n:
    if l <= num <= u:
        c += 1

print(c)

4

Explanation:

• Loop iterates through each number in the list n and checks if it falls within specified range [l, u].
• For each number that meets condition counter c is incremented ultimately giving count of numbers within range

Using numpy

We use numpy to create an array of numbers. We then use a condition to filter out the numbers within the range and numpy.sum() counts how many elements satisfy that condition.

import numpy as np

# Using numpy for large datasets
n = np.array([5, 15, 25, 35, 45, 55, 65, 75])
l = 20
u = 60

# Count numbers within the range using numpy
c = np.sum((n >= l) & (n <= u))

print(c)  

4

Explanation:

• Expression (n >= l) & (n <= u) generates a boolean array indicating which numbers are within the range.
• np.sum() counts the True values, giving the total number of numbers within the range.