📘 Lesson  ·  Lesson 81

Map, Filter, Reduce

Functional Tools

💡 At a Glance

map, filter and reduce apply a function to a whole list without writing loops — often used with lambda.

map() — transform each

Python
nums = [1, 2, 3, 4]
squared = list(map(lambda x: x*x, nums))
print(squared)
[1, 4, 9, 16]

filter() — keep some

Python
nums = [1, 2, 3, 4, 5, 6]
even = list(filter(lambda x: x % 2 == 0, nums))
print(even)
[2, 4, 6]

reduce() — combine to one

Python
from functools import reduce
nums = [1, 2, 3, 4]
total = reduce(lambda a, b: a + b, nums)
print(total)
10

Summary

  • map transforms each item, filter keeps matching items, reduce combines to one value.
  • Often paired with lambda for short functions.
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