Not sure I understood the above right. How would you write that using scala collections?
```
Tabs.groupBy( _.col1 ).flatMap{ case (key,group) => group.map( g => (g, group.map(_.col4).avg) ) }
```
If that's how you would write it with Scala collections, that's how you should be able to write it in Slick. Slick is first and foremost a Scala-to-SQL compiler, not an embedded DSL for SQL, eventhough we need some extensions to the Scala standard library for features, which it doesn't code, e.g. joins.