Simple combine using aggregate 'algorithm'

* changes the 'combine' result from a single array to an array of arrays
* all items in a nested array are of equal priority

I am pretty sure we'll want the result to be an array of arrays no matter the algorithm we choose, since ideas will often have matching priority. Calling this version of combine 'aggregate', which didn't actually give the result I thought it would - going to try and read up on 'fixed radius nearest neighbors' that Jeramy talked about before Tuesdays meetup