21 lines
551 B
Markdown
21 lines
551 B
Markdown
---
|
|
title: average_by
|
|
tags: math,list,intermediate
|
|
---
|
|
|
|
Calculates the average of a list, after mapping each element to a value using the provided function.
|
|
|
|
- Use `map()` to map each element to the value returned by `fn`.
|
|
- Use `sum()` to sum all of the mapped values, divide by `len(lst)`.
|
|
- Omit the last argument, `fn`, to use the default identity function.
|
|
|
|
```py
|
|
def average_by(lst, fn = lambda x: x):
|
|
return sum(map(fn, lst), 0.0) / len(lst)
|
|
```
|
|
|
|
```py
|
|
average_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda x: x['n'])
|
|
# 5.0
|
|
```
|