API Design Review: Aggregate and Math Functions

[benjchristensen]

Several operators on rx.Observable are intended for aggregation and potentially dangerous on long-running or infinite Observables. Similar to how blocking operators were moved to BlockingObservable it has been suggested that aggregation operators be collected into an AggregateObservable or something similarly named. This could be further broken into AggregateObservable and NumberObservable for ones specifically operating on numbers as the type would be <? extends Number> rather than <T>.

Some of these operators include:

• average*
• max (add maxBy (keySelector))
• min (add minBy)
• sum*
• contains
• count
• longCount
• toList
• reduce

/cc @headinthebox and @jhusain

[akarnokd]

Average, min, max and sum went into rxjava-math. Do we want to move the rest too? From the rest, I would rarely want to count the elements in a stream.

[headinthebox]

Agreed, we should not lead people towards reducing streams to single values.

[benjchristensen]

We still have:

• contains
• count
• longCount
• toList
• reduce

@headinthebox @akarnokd Should we leave these?

It seems that toList and reduce would be pretty jarring to remove. People get what they ask for on those. The contains and count are trivial and don't bother me being in the API.

I suggest we leave these 4.

[headinthebox]

Except for .ToList which I do often use, I'm happy to remove the others, but happy to keep them as well.

[benjchristensen]

I think we just leave them. They don't bother me. Closing this out.