30-seconds-of-code/snippets/python/s/sum-by.md

title, type, language, tags, cover, dateModified

title	type	language	tags	cover	dateModified
Sum list based on function	snippet	python	math list	horse-sunset	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