Aggregate functions such as `sum`

, `max`

etc. are readily available in Datomic's Datalog implementation. They are written in the `:find`

clause in your query:

```
[:find (max ?date)
:where
...]
```

An aggregate function collects values from multiple datoms and returns

- A single value:
`min`

,`max`

,`sum`

,`avg`

, etc. - A collection of values:
`(min n ?d)`

`(max n ?d)`

`(sample n ?e)`

etc. where`n`

is an integer specifying the size of the collection.

Given a collection of actors and (the now familiar) ratings data. Find the average rating for each actor. The query should return the actor name and the `avg`

rating.