Transform inverse mapping

[monfera]

• generating original points for transform results so that, upon interaction such as crossfiltering, the original (constituent) points can be recovered
• cascading these points through a (purportedly) arbitrary sequence of filter and aggregation steps (groupby not yet supported)
• adding test cases for these (also, we didn't have heterogeneous transforms testing with both filter and aggregate in the past)

There's still so much to do (PS: now documented the follow-up issue #2128); eg. more test cases; covering groupBy and sort. There's plenty of things to iterate on here.

On the pro side, the code change is rather small in terms of lines; also, the logic didn't need to change. So it's an add-on patch rather than anything heavy.

[alexcjohnson]

Since this isn't a real attribute but we're putting it back into fullData lets give it an _ - ie opts._indexToPoints.

[alexcjohnson]

Thanks for testing this! Nice to see indexToPoints cascade through the transforms.

[alexcjohnson]

_ is the only blocking comment, this looks great. Really clean and easy!

With this in place you can get what you need for crossfiltering, and nothing you did will need to change as we extend this, so I'm all for merging this with only that change.

But to use this mapping, you have to dive into _fullData and look for transforms. Seems like it would be more powerful if this were already part of the event data. I'm not quite sure the right way to do this though... possibly just attach a new attribute like event.points[i].inputPointNumbers? If there are no transforms this would just be [pointNumber] or pointNumbers, but if there are, it would map whichever of those exists through _indexToPoints? That way you could always just use inputPointNumbers. Also since any trace type could have a transform (and at this point all or nearly all types produce pointNumber(s) fields), it would be nice to find a clean way to apply this to all events consistently. But again, lets do that in a separate PR. Really great idea to go in this direction, and I'm pleased that it's turning out to be pretty straightforward to implement!

[alexcjohnson]

Very nice, thanks! 💃