Count positive and negative numbers in a list in Python program

In this article, we will learn how to count positive and negative numbers in a Python list using different approaches. We'll explore various methods from simple loops to more advanced functional programming techniques.

Problem statement ? We are given a list, we need to count positive and negative numbers in it and display them.

Using For Loop

The most straightforward approach is to iterate through each element and check if it's positive or negative using a for loop ?

numbers = [1, -2, -4, 6, 7, -23, 45, 0]
pos_count, neg_count = 0, 0

for num in numbers:
    if num >= 0:
        pos_count += 1
    else:
        neg_count += 1

print("Positive numbers in the list:", pos_count)
print("Negative numbers in the list:", neg_count)

Positive numbers in the list: 5
Negative numbers in the list: 3

Using While Loop

Alternatively, we can use a while loop with an index to iterate through the list ?

numbers = [1, -2, -4, 6, 7, -23, 45, 0]
pos_count, neg_count = 0, 0
index = 0

while index < len(numbers):
    if numbers[index] >= 0:
        pos_count += 1
    else:
        neg_count += 1
    index += 1

print("Positive numbers in the list:", pos_count)
print("Negative numbers in the list:", neg_count)

Positive numbers in the list: 5
Negative numbers in the list: 3

Using Lambda Functions

We can use filter() with lambda expressions to separate positive and negative numbers, then count them ?

numbers = [1, -2, -4, 6, 7, -23, 45, 0]

pos_count = len(list(filter(lambda x: x >= 0, numbers)))
neg_count = len(list(filter(lambda x: x < 0, numbers)))

print("Positive numbers in the list:", pos_count)
print("Negative numbers in the list:", neg_count)

Positive numbers in the list: 5
Negative numbers in the list: 3

Using List Comprehension

List comprehension provides a concise way to count positive and negative numbers ?

numbers = [1, -2, -4, 6, 7, -23, 45, 0]

pos_count = len([x for x in numbers if x >= 0])
neg_count = len([x for x in numbers if x < 0])

print("Positive numbers in the list:", pos_count)
print("Negative numbers in the list:", neg_count)

Positive numbers in the list: 5
Negative numbers in the list: 3

Comparison

Conclusion

All methods effectively count positive and negative numbers in a list. The for loop approach is most readable for beginners, while list comprehension offers the most Pythonic solution. Choose based on your coding style and requirements.