18 lines
429 B
Markdown
18 lines
429 B
Markdown
---
|
|
title: sum_by
|
|
tags: 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, use `sum()` to return the sum of the values.
|
|
|
|
```py
|
|
def sum_by(lst, fn):
|
|
return sum(map(fn,lst))
|
|
```
|
|
|
|
```py
|
|
sum_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda v : v['n']) # 20
|
|
```
|