Feature request: Table.to_group should accept block

[Gregory Brown]

we used to have something like

table.create_group("even") { |r| r.a % 2 == 0 }

We now have something like:

table.to_group("even")

but it only converts the entire table to a group.

Should we let it accept a block? I can see that as being potentially
handy, especially if you wanted to build up a custom Grouping via a
series of arbitrary blocks.

Mike et. al, what do you think?