BudJoin#rights and BudJoin#lefts don't return BudCollections

[jhellerstein]

As a result you can't cascade to BudCollection#argmin or BudCollection#group, etc.

[neilconway]

This should be easily to fix; I'll take a look tomorrow morning.

BTW, this sort of property is pretty fragile (especially given the Ruby style of omitting an explicit return statement). We should probably document it clearly when an interface method is expected to return a particular value.

[neilconway]

This actually doesn't seem that easy to (cleanly) fix. The problem is that lefts currently returns an Array constructed by calling map, rather than a BudCollection. We'll need to wrap the Array inside a BudCollection, which should be doable; it would be nice to avoid a deep copy of the actual data, which I think we can also do.

BTW, doesn't exactly the same problem occur if you just call map on a BudCollection and expect the result to be a BudCollection?

[neilconway]

Peter will take a look at this. BTW, here's a partial test case for the problem:

class ChainJoinsWithGroup
  include Bud

  state do
    scratch :s1, [:a, :b]
    scratch :s2, [:a, :b]
    scratch :r1, [:key] => [:val_min]
    scratch :r2, [:key] => [:val_max]
  end

  bootstrap do
    s1 <= [[5, 10], [5, 12], [8, 19], [8, 20]]
    s2 <= [[5, 5], [8, 25]]
  end

  bloom do
    r1 <= (s1 * s2).lefts(:a => :a).group([:a], min(:b))
    r2 <= (s1 * s2).rights(:a => :a).group([:a], max(:b))
  end
end

[jhellerstein]

add flat_map to the list of methods that need to produce a BudCollection. just tripped across a bug resulting from that (which I'm working around for now.)