[R] union type support

[asfimport]

Reporter: Romain Francois / @romainfrancois

_{Note: This issue was originally created as ARROW-3812. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
This seems lower priority than many other things in the 1.0.0 backlog

[thisisnic]

I think this is resolved now; if not, feel free to reopen

[amoeba]

Hi @thisisnic, I think this issue might have been a placeholder for supporting the Arrow Union types, which I don't think we support yet. Just guessing based on the issue reporter and the author/timing of

arrow/r/src/datatype.cpp

Lines 110 to 116 in d2a8b78

	// No R6 classes are defined for:
	// INTERVAL
	// SPARSE_UNION
	// DENSE_UNION
	// MAP
	// EXTENSION
	// DURATION

We do have a binding for dplyr::union though. What do you think?

[thisisnic]

Thanks @amoeba; that makes a lot of sense and you're probably right. Not sure it's worth keeping a ticket hanging around given nobody's working on it, and there's no user interest though?

[amoeba]

Yeah, that's fine. I'll update the title though.