30-seconds-of-code/snippets/sum_by.md

title, tags, expertise, firstSeen, lastUpdated

title	tags	expertise	firstSeen	lastUpdated
Sum list based on function	math,list	beginner	2019-08-21T08:30:04+03:00	2020-11-02T19:28:35+02:00

Calculates the sum of a list, after mapping each element to a value using the provided function.

• Use map() with fn to map each element to a value using the provided function.
• Use sum() to return the sum of the values.

def sum_by(lst, fn):
  return sum(map(fn, lst))

sum_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda v : v['n']) # 20