Can we do this as
```
nearestCenters groupBy { case (cid, _) => cid } reduce { (z, v) => (z._1, z._2 + v._2) } map { case (cid, pSum) => cid -> pSum.toPoint() }
```
This is also a candidate for a built-in aggregate function.
```
nearestCenters groupBy { case (cid, _) => cid } aggregate ( SUM, {_._2 } ) map { case (cid, pSum) => cid -> pSum.toPoint() }
```