David Anthoff

See [here](https://discourse.julialang.org/t/query-jl-group-dataframe-by-abstracttype-gives-method-error/15501).

[TypeScript 2.1](https://blogs.msdn.microsoft.com/typescript/2016/12/07/announcing-typescript-2-1/) seems to have some features that would really help this package. Investigate that.

If you have a question or are unsure if the behavior you're experiencing is a bug, please search or post to the Data domain on the julia Discourse site: https://discourse.julialang.org/c/domain/data....

``$foo`` could be translated into ``_.foo`` (or rather really ``i->i.foo``). Thanks to @nalimilan for bringing up the ``$`` option over on the [forums](https://discourse.julialang.org/t/suggestion-move-dataframes-plotting-into-stdlib/9115/36?u=davidanthoff).

The ``default_if_empty`` strategy doesn't work in that case.

Consider allowing joins on different types

2

Right now the types of the key must match, that could be relaxed.