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30-seconds-of-code/snippets/max_by.md
2022-06-09 13:00:34 +03:00

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---
title: Max list value based on function
tags: math,list
expertise: beginner
cover: blog_images/digital-nomad-3.jpg
firstSeen: 2019-08-20T15:42:41+03:00
lastUpdated: 2020-11-02T19:28:27+02:00
---
Returns the maximum value 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 `max()` to return the maximum value.
```py
def max_by(lst, fn):
return max(map(fn, lst))
```
```py
max_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda v : v['n']) # 8
```