But my point is that Aggregate and reduce can handle that in this case because they both can simply add to the PriceAndRows instance incrementally. You can sum

But my point is that Aggregate and reduce can handle that in this case because they both can simply add to the PriceAndRows instance incrementally. You can sum the total and build the list in the body of the Aggregate/reduce method. Teeing is pointless here. There's no need to use another collector.