Provide a way to coalesce the entries in a RangeMap

[dimo414]

RangeMap doesn't coalesce connected ranges (by design), and it would be nice if there were a built-in way to coalesce connected ranges if they have the same value. For example:

{[0..1): 1, [1..2): 1, [2..3): 2}

Is roughly equivalent to:

{[0..2): 1, [2..3): 2}

And it can be both a time and space savings to be working with a smaller data structure. Particularly for a case such as a RangeMap built up from Range.singleton() keys a coalesced() operation could save a lot of resources.

[lowasser]

Could you live with a RangeMaps.coalesced operation, that is, a one-off coalesce operation rather than doing it online?

[dimo414]

Definitely; I'd expect it to be a copy operation as a live view would eliminate the benefit of reducing the underlying number of ranges in use (and probably be much more complex to implement). ImmutableRangeMap.coalescedFrom(RangeMap) could also work.

[dimo414]

We opted to add a mutating .putCoalescing() operation rather than a copy or a view. Please let us know if you have a use case for which this isn't sufficient.

[perceptron8]

@dimo414 I'd like to report "merging + coalescing" as a general use case, that .putCoalescing doesn't support at all. I think that .coalesced() (or similarly named) method could work nicely with #6822, or at least as a way to "clean-up" after series of RangeMap.merge calls (see #3641 for details if you like).