Addresses #237. Provides a way to project the entire dataset into a s…

[imarios]

…ingle column.

[codecov-io]

Codecov Report

Merging #238 into master will increase coverage by 0.12%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #238      +/-   ##
==========================================
+ Coverage   96.84%   96.96%   +0.12%     
==========================================
  Files          52       52              
  Lines         855      858       +3     
  Branches       10       12       +2     
==========================================
+ Hits          828      832       +4     
+ Misses         27       26       -1

Impacted Files	Coverage Δ
...ataset/src/main/scala/frameless/TypedDataset.scala	100% <100%> (ø)	⬆️
...c/main/scala/frameless/TypedDatasetForwarded.scala	74.28% <0%> (+2.85%)	⬆️

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[OlivierBlanvillain]

Not convinced about the name. How is this done in vanilla?

[imarios]

@OlivierBlanvillain I am not super fun of the name either, but I couldn't think of anything better ... Do you have anything else we might try?

To the best of my knowledge vanilla doesn't have this. I can see it being useful though, say you want to add an extra column to a dataset, doing this you don't have to result to a Tuple and you don't have to define a new type. E.g.,

d: TypedDataset[Foo]
d.select(d.toCol, myudf(d('a) * 2)): TypedDetaset[(Foo,Long)] // Foo plus the new column we added

[imarios]

@OlivierBlanvillain @frosforever any better name suggestions for this?

[frosforever]

I can't really think of a better name. Only time I've ever needed to do something like this I used groupBy / groupByKey instead. Sorry I'm not much help here.