---
title: Max list value based on function
tags: math,list
cover: digital-nomad-3
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
```