Four Quick Python Tricks to Count the Number of 1s in a List

The author, a Python enthusiast, addresses a fan's basic Python question about counting the number of 1s in an array.

Implementation Idea

The solution can use len(), list comprehensions, Counter, or the count() function.

Implementation

Method One

This method, contributed by a Beijing algorithm expert, uses an anonymous function and filter.

a = [1,0,2,0,1]
b = list(filter(lambda x: x==1, a))
print(b)
print(f"1的个数：{len(b)}")

Method Two

This method, from a Guangzhou data analysis expert, uses a list comprehension.

a = [1, 0, 2, 0, 1]
b = [x for x in a if x == 1]
print(len(b))
print(f"1的个数：{len(b)}")

Method Three

This method uses Counter to count each element and displays the result as a dictionary.

from collections import Counter
a = [1, 0, 2, 0, 1]
b = Counter(a)
print(b)

Method Four

This method uses the list count() method.

a = [1, 0, 2, 0, 1]
print(a.count(1))
print(f"1的个数：{a.count(1)}")

Conclusion

The article presents four different ways to count the occurrences of 1 in a list, demonstrating the use of anonymous functions, filter, list comprehensions, Counter, and count methods, helping the reader solve the basic problem.