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How do I convert Option [String] to Option [Int]?

I am reading and parsing a json file. One of the fields in the json file is Nullable. It either returns a string of digits or Null. I need to convert a string to int. I can convert from String to Option [Int] with the below code, but could not convert from Option [String] to Option [Int]

 def toInt(userId: String):Option[Int] = {
  try {
    Some(userId.toInt)
  } catch {
    case e:Exception => None
  }
}

val user = toInt("abc")

What changes do I need to make?

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3 answers 


import util.Try

def toInt(o: Option[String]): Option[Int] =
  o.flatMap(s => Try(s.toInt).toOption)

Examples:



scala> toInt(None)
res0: Option[Int] = None

scala> toInt(Some("42"))
res1: Option[Int] = Some(42)

scala> toInt(Some("abc"))
res2: Option[Int] = None
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Option(userId).map(_.toInt)


Use Option

instead Some

. Then use map

to convert it toInt

+3


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You need map

Option

to do something with the possible contained value. In the context of your code, I would use flatMap

since the current method returns Option

, so we have to flatten out what would be nested Option

.

def toInt(userIdOpt: Option[String]): Option[Int] = userIdOpt flatMap { userId =>
  try {
    Some(userId.toInt)
  } catch {
    case e:Exception => None
  }
}

scala> val u = Option("2")
u: Option[String] = Some(2)

scala> toInt(u)
res0: Option[Int] = Some(2)

scala> toInt(Some("a"))
res4: Option[Int] = None

We can shorten this by using Try

.

import scala.util.Try

def toInt(userIdOpt: Option[String]): Option[Int] =
    userIdOpt.flatMap(a => Try(a.toInt).toOption)

Try(a.toInt)

returns a Try[Int]

where a successful conversion will be Success[Int]

and a failed conversion (not an integer) will be Failure[Throwable]

. Try

has a very handy method called toOption

, which converts Success(a)

to Some(a)

and Failure

to None

what we want.

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