FAQ: Functional Programming - Reducing a Mapped Collection

This community-built FAQ covers the " Reducing a Mapped Collection" exercise from the lesson “Functional Programming”.

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This exercise can be found in the following Codecademy content:

[Beta] Learn Advanced Python 3

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In exercise 2 on page 7 the solution is given as “r = reduce(lambda x, y: x + y2, nums)", but it should be "r = reduce(lambda x, y: x2 + y**2, nums)”.

I agree that the solution isn’t quite right but that squares both sides in the reduction which wouldn’t be right either. The given solution but with an initializer https://docs.python.org/3/library/functools.html#functools.reduce of 0 is the way to go.

import functools import operator nums = (2, 4, 6, 8) original = functools.reduce(lambda x, y: x + y, map(lambda q: q**2, nums)) given_solution = functools.reduce(lambda x, y: x + y**2, nums) square_both = functools.reduce(lambda x, y: x** 2 + y**2, nums) print(original, given_solution, square_both) initialised = functools.reduce(lambda x, y: x + y**2, nums, 0) print(original, initialised)
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