scala Map with Option/Some gives match error - scala

Question

The following code is producing run time error as below. Could reason why the following error. Please explain.
Exception in thread "main" scala.MatchError: Some(Some(List(17))) (of class scala.Some)
at com.discrete.CountingSupp$.$anonfun$tuplesWithRestrictions1$1(CountingSupp.scala:43)
def tuplesWithRestrictions1(): (Int, Map[Int, Option[List[Int]]]) = {
val df = new DecimalFormat("#")
df.setMaximumFractionDigits(0)
val result = ((0 until 1000) foldLeft[(Int, Map[Int, Option[List[Int]]])] ((0, Map.empty[Int, Option[List[Int]]]))) {
(r: (Int, Map[Int, Option[List[Int]]]), x: Int) => {
val str = df.format(x).toCharArray
if (str.contains('7')) {
import scala.math._
val v = floor(log10(x)) - 1
val v1 = (pow(10, v)).toInt
val m: Map[Int, Option[List[Int]]] = (r._2).get(v1) match {
case None => r._2 + (v1 -> Some(List(x)))
case Some(xs: List[Int]) => r._2 updated(x, Some(x::xs))
}
val f = (r._1 + 1, m)
f
} else r
}
}
result
}

Answer 1

Return type of .get on map is
get(k: K): Option[V]
Scala doc
/** Optionally returns the value associated with a key.
*
* #param key the key value
* #return an option value containing the value associated with `key` in this map,
* or `None` if none exists.
*/
def get(key: K): Option[V]
Now,
r._2.get(v1) returns an option of Value. So the final return type would be Option[Option[List[Int]]].
You are trying to pattern match for Option[T] but the real value type is Option[Option[Int]] which is not captured in the match.
Use r._2(v1) to extract the value and match. Throws exception when v1 is not found in map.
Match inside map providing default value.
r._2.get(k1).map {
case None => r._2 + (v1 -> Some(List(x)))
case Some(value) => r._2 updated(x, Some(x::xs))
}.getOrElse(defaultValue)

Answer 2

def tuplesWithRestrictions1(): (Int, Map[Int, List[Int]]) = {
val df = new DecimalFormat("#")
df.setMaximumFractionDigits(0)
val result = ((0 until 1000) foldLeft[(Int, Map[Int, List[Int]])] ((0, Map.empty[Int, List[Int]]))) {
(r: (Int, Map[Int, List[Int]]), x: Int) => {
val str = df.format(x).toCharArray
if (str.contains('7')) {
import scala.math._
val v = floor(log10(x))
val v1 = (pow(10, v)).toInt
val m: Map[Int, List[Int]] = (r._2).get(v1) match {
case Some(xs: List[Int]) => r._2 updated(v1, x :: xs)
case None => r._2 + (v1 -> List(x))
}
val f = (r._1 + 1, m)
f
} else r
}
}
result
}