allow selector => fun1 => fun2 in select and combine #2207
Description
This is an extension for the future proposal.
In the form selector => fun1 => fun2 we could allow for fun2 in addition to requiring the last argument to be a Symbol or a string.
In this way we could allow for dynamic generation of target column names. The question is what API for fun2 should be. Should it take only a list of source column names or also fun1 or output of fun1. This is to be worked out for later.