Scala groupBy of a tuple to calculate stock basis - scala

Question

I am working on an exercise to calculate stock basis given a list of stock purchases in the form of thruples (ticker, qty, stock_price). I've got it working, but would like to do the calculation part in more of a functional way. Anyone have an answer for this?
// input:
// List(("TSLA", 20, 200),
// ("TSLA", 20, 100),
// ("FB", 10, 100)
// output:
// List(("FB", (10, 100)),
// ("TSLA", (40, 150))))
def generateBasis(trades: Iterable[(String, Int, Int)]) = {
val basises = trades groupBy(_._1) map {
case (key, pairs) =>
val quantity = pairs.map(_._2).toList
val price = pairs.map(_._3).toList
var totalPrice: Int = 0
for (i <- quantity.indices) {
totalPrice += quantity(i) * price(i)
}
key -> (quantity.sum, totalPrice / quantity.sum)
}
basises
}

Answer 1

This looks like this might work for you. (updated)
def generateBasis(trades: Iterable[(String, Int, Int)]) =
trades.groupBy(_._1).mapValues {
_.foldLeft((0,0)){case ((tq,tp),(_,q,p)) => (tq + q, tp + q * p)}
}.map{case (k, (q,p)) => (k,q,p/q)} // turn Map into tuples (triples)

Answer 2

I came up with the solution below. Thanks everyone for their input. I'd love to hear if anyone had a more elegant solution.
// input:
// List(("TSLA", 20, 200),
// ("TSLA", 10, 100),
// ("FB", 5, 50)
// output:
// List(("FB", (5, 50)),
// ("TSLA", (30, 166)))
def generateBasis(trades: Iterable[(String, Int, Int)]) = {
val groupedTrades = (trades groupBy(_._1)) map {
case (key, pairs) =>
key -> (pairs.map(e => (e._2, e._3)))
} // List((FB,List((5,50))), (TSLA,List((20,200), (10,100))))
val costBasises = for {groupedTrade <- groupedTrades
tradeCost = for {tup <- groupedTrade._2 // (qty, cost)
} yield tup._1 * tup._2 // (trade_qty * trade_cost)
tradeQuantity = for { tup <- groupedTrade._2
} yield tup._1 // trade_qty
} yield (groupedTrade._1, tradeQuantity.sum, tradeCost.sum / tradeQuantity.sum )
costBasises.toList // List(("FB", (5, 50)),("TSLA", (30, 166)))
}