Lack of API-docs makes it very hard to onboard users

[holgerbrandl]

It seems to be by design to split documentation and implementation. However, when working with the library a java-doc would be very helpful. Maybe by providing pointers into HTML documentation, but maybe also a more classical API documentation to guide development. Currently, because the library is rather complex and has grown considerably, it is a hard learning experience.

This would also allow documenting the numerous parameters that are not reflected in the guide, such as moveToTop in groupBy to give one example. Parameter documentation IMHO works best in place via javadoc, because it's the closest to the actual use/call-site.

Example to demonstrate the problem:

[Jolanrensen]

Agreed, similar to https://github.com/Kotlin/dataframe/issues/29 We'll definitely add KDocs before a 1.0 release.