I have the following use case, in which I am iterating multiple times on the same collection, and every time I find a different item in that collection.
class Foo(policyToData: Map[String, MyClass]){
val milk: Option[MyClass] = policyToData.values.find(_.`type` == Milk)
val meat: Option[MyClass] = policyToData.values.find(_.`type` == Meat)
val bread: Option[MyClass] = policyToData.values.find(_.`type` == Bread)
val other: List[MyClass] = policyToData.values.filter(_.`type` == Other).toList
}
Is there a better way to do it? with one iteration?
If it's a large collection, folding into a map means you only build the collection of interest.
scala> case class C(name: String)
defined class C
scala> val cs = List(C("milk"),C("eggs"),C("meat"))
cs: List[C] = List(C(milk), C(eggs), C(meat))
scala> cs.foldLeft(Map.empty[String,C]) {
| case (m, c @ C("milk" | "meat")) if !m.contains(c.name) => m + (c.name -> c)
| case (m, _) => m }
res5: scala.collection.immutable.Map[String,C] = Map(milk -> C(milk), meat -> C(meat))
then
scala> val milk = res5("milk")
milk: C = C(milk)
scala> val bread = res5.get("bread")
bread: Option[C] = None
The original groupBy
solution was deleted because someone commented that it does extra work, but in fact it's a straightforward expression, if creating the intermediate Map of Lists is OK.
scala> cs.groupBy(_.name)
res0: scala.collection.immutable.Map[String,List[C]] = Map(meat -> List(C(meat)), eggs -> List(C(eggs)), milk -> List(C(milk)))
scala> res0.get("milk").map(_.head)
res1: Option[C] = Some(C(milk))
scala> res0.get("bread").map(_.head)
res2: Option[C] = None
or
scala> cs.filter { case C("milk" | "meat") => true case _ => false }.groupBy(_.name)
res4: scala.collection.immutable.Map[String,List[C]] = Map(meat -> List(C(meat)), milk -> List(C(milk)))
groupBy
will do it:
val byType = list.groupBy(_.type).withDefaultValue(Nil)
val milk = byType(Milk).headOption
val other = byType(Other)
Etc ...
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