[TOC] ## Solution --- [Pandas](#pandas) [Database](#database) # pandas ### Approach: Group By and Count #### Intuition In pandas, we can use the `.groupby` function on the `'actor_id'` and `'director_id'` columns and then count the number of instances per group using the `.size()` function. We then filter out the groups that have a count of at least `3`. #### Algorithm To solidify the intuition behind the algorithm, let's first look at an example: The original table `actor_director`:

actor_id	director_id	timestamp
1	1	0
1	1	1
1	1	2
1	2	3
1	2	4
2	1	5
2	1	6

The following table is obtained by grouping `actor_id` and `director_id`, and then filtered to include only those groups with a count of at least 3.

actor_id	director_id
1	1

Note that the returned DataFrame contains only the `actor_id` and `director_id` columns. #### Implementation ```python3 import pandas as pd def actors_and_directors(actor_director: pd.DataFrame) -> pd.DataFrame: cnts = actor_director.groupby(['actor_id', 'director_id']).size().reset_index(name='counts') return cnts[cnts['counts'] >= 3][['actor_id', 'director_id']] ```
--- # database ### Approach: Group By and Count #### Intuition In SQL, the query to find the actor-director pairs that have cooperated at least three times involves grouping by the `actor_id` and `director_id` and then filtering out the pairs that have a count of at least 3. #### Algorithm To solidify the intuition behind the algorithm, let's first look at an example: The original table `ActorDirector`:

actor_id	director_id	timestamp
1	1	0
1	1	1
1	1	2
1	2	3
1	2	4
2	1	5
2	1	6

The following table is obtained by grouping `actor_id` and `director_id`, and then filtered to include only those groups with a count of at least 3.

actor_id	director_id
1	1

Note that we only select the `actor_id` and `director_id` columns. #### Implementation ```sql SELECT actor_id, director_id FROM ActorDirector GROUP BY actor_id, director_id HAVING COUNT(timestamp) >= 3; ```

Actors and Directors Who Cooperated At Least Three Times

Problem Description

Problem Description

Answer Panel