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

title, tags

title	tags
sum_by	math,list,function,beginner

Returns 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, convert to a list and use sum() to return the sum of the values.

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

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