﻿ Python: Get the difference between two given lists, after applying the provided function to each list element of both - w3resource # Python: Get the difference between two given lists, after applying the provided function to each list element of both

## Python List: Exercise - 222 with Solution

Write a Python program to get the difference between two given lists, after applying the provided function to each list element of both.

• Create a set, using map() to apply fn to each element in b.
• Use a list comprehension in combination with fn on a to only keep values not contained in the previously created set, _b.

Sample Solution:

Python Code:

``````def difference_by(a, b, fn):
_b = set(map(fn, b))
return [item for item in a if fn(item) not in _b]
from math import floor
print(difference_by([2.1, 1.2], [2.3, 3.4], floor))
print(difference_by([{ 'x': 2 }, { 'x': 1 }], [{ 'x': 1 }], lambda v : v['x']))
```
```

Sample Output:

```[1.2]
[{'x': 2}]
```

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## Python: Tips of the Day

Floor Division:

When we speak of division we normally mean (/) float division operator, this will give a precise result in float format with decimals.

For a rounded integer result there is (//) floor division operator in Python. Floor division will only give integer results that are round numbers.

```print(1000 // 300)
print(1000 / 300)```

Output:

```3
3.3333333333333335```