Named intermediate Datasets

case class Foo(bar: Int, baz: String, bal: Boolean)
val ds: TypedDataset[Foo]

This is nicely named and typed! However, after a select, the names are completely lost:

val ds1: TypedDataset[Tuple2[Int, String]] = ds.select(ds('bar), ds('baz))

The best one can do with the current API is to define a new case class for the intermediate representation, and use .as[] to get a ds1 with useful columns names.

Somes idea to workaround this issue:

• Use a macro to generate a case classes "on the fly", something like this:

  ds.selectNamed(ds('bar), ds('baz))
  // Expends to
  case class FooBarBaz(bar: Int, baz: String)
  ds.selectNamed(ds('bar), ds('baz)).as[FooBarBaz]
  

• Instead of TupleN, type the resulting Dataset with a shapeless record and update.

Review the TypedDataset.select API and its TupleN result described in the issue, then compare the proposed macro-generated case class and shapeless-record approaches. Done means an intermediate selection such as ds.select(ds('bar), ds('baz)) preserves usable column names without requiring a manually defined case class or .as conversion; the issue names no files or tests.