20 lines
648 B
Markdown
20 lines
648 B
Markdown
---
|
|
title: difference_by
|
|
tags: list,function,intermediate
|
|
---
|
|
|
|
Returns the difference between two lists, after applying the provided function to each list element of both.
|
|
|
|
Create a `set` by applying `fn` to each element in `b`, then use list comprehension in combination with `fn` on `a` to only keep values not contained in the previously created set, `_b`.
|
|
|
|
```py
|
|
def difference_by(a, b, fn):
|
|
_b = set(map(fn, b))
|
|
return [item for item in a if fn(item) not in _b]
|
|
```
|
|
|
|
```py
|
|
from math import floor
|
|
difference_by([2.1, 1.2], [2.3, 3.4],floor) # [1.2]
|
|
difference_by([{ 'x': 2 }, { 'x': 1 }], [{ 'x': 1 }], lambda v : v['x']) # [ { x: 2 } ]
|
|
``` |