How does find function in Map work in Scala? - scala

Question

I am new to Scala. This is the code that I have written.
object Main extends App {
val mp: Map[String, String] = Map[String, String]("a"->"a", "b"->"b", "c"->"c", "d"->"d")
val s: Option[(String, String)] = mp.find((a: String, b: String) => {
if(a == "c" && b == "c") {
true
}
else {
false
}
})
println(s)
}
I am getting the following error.
error: type mismatch;
found : (String, String) => Boolean
required: ((String, String)) => Boolean
What am I doing wrong?

Answer 1

You need to change
mp.find((a: String, b: String) =>
to either
mp.find(((a: String, b: String)) =>
or
mp.find( case (a: String, b: String) =>
What you have coded is a function expecting two parameters, but you will only be passing in one, which is a Pair (also called Tuple2). The extra braces and the case keyword are ways of specifying that you are only passing in the one parameter, which is an instance of a Pair.

Answer 2

The problem is that find expects a function that takes a single argument, a Tuple2 in this case and returns a Boolean: ((String, String)) => Boolean. However, what you have there is a function that takes two args a and b, not a tuple (brackets matter): (String, String) => Boolean.
Here is one way to fix it. In this case I use pattern matching to extract arguments:
object Main extends App {
val mp: Map[String, String] = Map[String, String]("a"->"a", "b"->"b", "c"->"c", "d"->"d")
val s: Option[(String, String)] = mp.find{ case(a, b) => a == "c" && b == "c" }
println(s)
}
alternatively you could also do:
val s: Option[(String, String)] = mp.find(t => t._1 == "c" && t._2 == "c")
Either would print:
Some((c,c))