Question

有人可以帮助我将其转换为flatMap或for -reherehension吗？我知道如何处理嵌套选项的更多琐碎场景。

    case class Person(name: String, signficantOther: Option[String])
    val nightclubPeoples : Option[Seq[Person]] = ???

    def significantOthers(nightClubPeoples : Option[Seq[Person]]) : List[String] = {
      nightclubPeoples match {
        case Some(x) => x map { y : Person => 
          y.significantOther match {
            case Some(z) => z
            case None => "No Signficant Other"
          }
        }.toList
        case None => Nil
      }
    }

Answer 1

我想我会使用折叠：

nightclubPeoples.fold[List[String]](Nil)(_.flatMap(_.signficantOther)(collection.breakOut))

Answer 2

正如我认为的那样，Sascha Kolberg的回答是更好的解决方案（只是在signficantOther为空时省略，即＆＃34; No Signficant Other＆＃34;不会在结果列表中< / strong>）因为你的问题你要求＆＃34;将其转换为flatMap或for-comprehension＆＃34;，所以代码如下。

case class Person(name: String, signficantOther: Option[String]) val nightClubPeopleOpt : Option[Seq[Person]] = Some(Person("name", Some("1")) :: Person("name1", None) :: Nil) def significantOthers(nightClubPeopleOpt : Option[Seq[Person]]) = { for { nightClubPeople <- nightClubPeopleOpt } yield { // scenario 1 // if signficantOther is empty, then it should be ignored // Answer -> List(1) nightClubPeople.flatMap(_.signficantOther).toList // scenario 2 // if signficantOther is empty, then we use the default "No Signficant Other" // Answer -> List(1, No Signficant Other) nightClubPeople.map { nightClubPerson => nightClubPerson.signficantOther.getOrElse("No Signficant Other") }.toList } }.getOrElse(Nil) println(significantOthers(nightClubPeopleOpt))

Answer 3

你走了：

nightclubPeoples.toSeq.flatMap(_.map(_.signficantOther.getOrElse("No Signficant Other")))

Answer 4

相对可读的直接转换是：

def significantOthers(nightClubPeoples : Option[Seq[Person]]): List[String] = {
  for {
    nightClubPeoples <- nightClubPeoples.toList
    person <- nightClubPeoples
  } yield person.significantOther.getOrElse("No Significant Other")
}

这里要注意的是我们将nightClubPeoples转换为预先列表，允许我们一直使用for for comprehension。

但是，当signficantOther为None时，我怀疑您确实希望列表中显示“无显着其他”。相反，它应该被忽略，这将使更简单：

def significantOthers(nightClubPeoples : Option[Seq[Person]]): List[String] = {
  for {
    nightClubPeoples <- nightClubPeoples.toList
    person <- nightClubPeoples
    significantOther <- person.significantOther
  } yield significantOther
}

嵌套选项Monad上的FlatMap或For-comprehension

4 个答案: