Scala Cast List of Any 到 Int 列表

Question

Given a List of Any:

val l = List(2.9940714E7, 2.9931662E7, 2.993162E7, 2.9931625E7, 2.9930708E7, 2.9930708E7, 2.9931477E7)

I need to cast each item to Int.

Works:

l(1).asInstanceOf[Double].toInt

Not:

l.foreach{_.asInstanceOf[Double].toInt}
> java.lang.String cannot be cast to java.lang.Double

If

l.foreach{_.asInstanceOf[String].toDouble.toInt}
> java.lang.Double cannot be cast to java.lang.String

I'm new to Scala. Please tell me what I'm missing. Why I can cast one item from list, but can't do this via iterator? Thanks!

Answer 1

Your given List is of type Double . You can use simply map operation to convert it to Int type. try following code,

val l: List[Double] = List(2.9940714E7, 2.9931662E7, 2.993162E7, 2.9931625E7, 2.9930708E7, 2.9930708E7, 2.9931477E7)

//simply map the list and use toInt
val intLst: List[Int] = l.map(_.toInt)

print(intLst)

//output
//List(29940714, 29931662, 29931620, 29931625, 29930708, 29930708, 29931477)

But suppose you have same List as List[Any] instead then you can use following to convert it to Int .

val l: List[Any] = List(2.9940714E7, 2.9931662E7, 2.993162E7, 2.9931625E7, 2.9930708E7, 2.9930708E7, 2.9931477E7)

val intLst: List[Int] = l.map(_.asInstanceOf[Double].toInt)

It will give same output as above.

Answer 2

It seems as if a String somehow ended up in your List l .

Given a list that is structured like this (with mixed integers, Double s, and String s):

val l = List[Any](2.9940714E7, 2.9931625E7, "2.345E8", 345563)

You can convert it to list of integers as follows:

val lAsInts = l.map {
  case i: Int => i
  case d: Double => d.toInt
  case s: String => s.toDouble.toInt
}

println(lAsInts)

This works for Double s, Int s and String s. If it still crashes with some exceptions during the cast, then you can add more cases. You can, of course, do the same in a foreach if you want, but in this case it wouldn't do anything, because you don't do anything in the body of foreach except casting. This has no useful side-effects (eg it prints nothing).

Another option would be:

lAsInts = l.map{_.toString.toDouble.toInt}

This is in a way even more forgiving to all kind of weird input, at least as long as all values are "numeric" in some sense.

However, this is definitely code-smell: how did you get a list with such a wild mix of values to begin with?