Replacing values from list of custom objects with map values - scala

Question

I have a quite odd problem to solve, I have a String, a custom Type and a Map of Maps.
The string needs to have a few values replaced based on mapping between a value in custom type (which is a key in the map of maps).
This is the current structure:
case class Students(favSubject: String)
val mapping: Map[String, Map[String, String]] = Map("John" -> Map("English" -> "Soccer"))
val studentInfo: List[Students] = List(Students("English"))
val data: String = "John is the favourite hobby"
I tried the following:
mapping.foldLeft(data){ case (outputString, (studentName, favSubject)) => outputString.replace(studentName, favSubject.getOrElse(studentInfo.map(x => x.favSubject).toString, "")) }
What I need to get is:
"Soccer is the favourite hobby"
What I get is:
" is the favourite hobby"
So looks like I am getting the map of maps traversal right but the getOrElse part is having issues.

Answer 1

What I would do, would be to first change the structure of mappings so it makes more sense for the problem.
val mapping: Map[String, Map[String, String]] = Map("John" -> Map("English" -> "Soccer"))
val mapping2 =
mapping.iterator.flatMap {
case (student, map) => map.iterator.map {
case (info, value) => (info, student, value)
}
}.toList
.groupBy(_._1)
.view
.mapValues { group =>
group.iterator.map {
case (_, student, value) => student -> value
}.toList
}.toMap
// mapping2: Map[String, List[(String, String)]] = Map("English" -> List(("John", "Soccer")))
Then I would just traverse the students informativo, making all the necessary replacements.
final case class StudentInfo(favSubject: String)
val studentsInformation: List[StudentInfo] = List(StudentInfo("English"))
val data: String = "John is the favourite hobby"
val result =
studentsInformation.foldLeft(data) { (acc, info) =>
mapping2
.getOrElse(key = info.favSubject, default = List.empty)
.foldLeft(acc) { (acc2, tuple) =>
val (key, replace) = tuple
acc2.replace(key, replace)
}
}
// result: String = "Soccer is the favourite hobby"

Answer 2

When you map() a List, you get a List back. It's toString has a format "List(el1,el2,...)". Surely you cannot use it as a key for your sub-map, you would want just el1.
Here is a version of the working code. It might not be a solution you are looking for(!), just a solution to your question:
case class Students(favSubject: String)
val mapping: Map[String, Map[String, String]] = Map("John" -> Map("English" -> "Soccer"))
val studentInfo: List[Students] = List(Students("English"))
val data: String = "John is the favourite hobby"
val res = mapping.foldLeft(data) {
case (outputString, (studentName, favSubjectDict)) =>
outputString.replace(
studentName,
favSubjectDict.getOrElse(studentInfo.map(x => x.favSubject).head, "?")
)
}
println(s"$res") //prints "Soccer is the favourite hobby"
val notMatchingSubject = studentInfo.map(x => x.favSubject).toString
println(s"Problem in previous code: '$notMatchingSubject' !== 'English'")
Try it here: https://scastie.scala-lang.org/flQNRrUQSXWPxSTXOPPFgA
The issue
It is a bit unclear why StudentInfo is a List in this form... If I guessed, it was designed to be a list of StudentInfo containing both, name and favSubject and you would need to search it by name to find favSubject. But it is just a guess.
I went with the simplest working solution, to get a .head (first element) of the sequence from the map. Which will always be "English" even if you add more Studends to the list.