Scala: batch process Map of index-based form fields - scala

Question

Part of a web app I'm working on handles forms that need to be bound to a collection of model (case class) instances. See this question
So, if I were to add several users at one time, form fields would be named email[0], email[1], password[0], password[1], etc.
Posting the form results in a Map[String, Seq[String]]
Now, what I would like to do is to process the Map in batches, by index, so that for each iteration I can bind a User instance, creating a List[User] as the final result of the bindings.
The hacked approach I'm thinking of is to regex match against "[\d]" in the Map keys and then find the highest index via filter or count; with that, then (0..n).toList map{ ?? } through the number of form field rows, calling the binding/validation method (which also takes a Map[String, Seq[String]]) accordingly.
What is a concise way to achieve this?

Answer 1

Assuming that:
All map keys are in form "field[index]"
There is only one value in Seq for each key.
If there is entry for "email[x]" than there is entry for "password[x]" and vice versa.
I would done something like this:
val request = Map(
"email[0]" -> Seq("alice#example.com"),
"email[1]" -> Seq("bob#example.com"),
"password[0]" -> Seq("%vT*n7#4"),
"password[1]" -> Seq("Bfts7B&^")
)
case class User(email: String, password: String)
val Field = """(.+)\[(\d+)\]""".r
val userList = request.groupBy { case (Field(_, idx), _) => idx.toInt }
.mapValues { userMap =>
def extractField(name: String) =
userMap.collect{case (Field(`name`, _), values) => values.head}.head
User(extractField("email"), extractField("password"))}
.toList.sortBy(_._1).map(_._2)
// Exiting paste mode, now interpreting.
request: scala.collection.immutable.Map[String,Seq[String]] = Map(email[0] -> List(alice#example.com),
email[1] -> List(bob#example.com), password[0] -> List(%vT*n7#4), password[1] -> List(Bfts7B&^))
defined class User
Field: scala.util.matching.Regex = (.+)\[(\d+)\]
userList: List[User] = List(User(alice#example.com,%vT*n7#4), User(bob#example.com,Bfts7B&^))