CODEWITHSUNDEEP
scalarecursiontypespattern-matching
Francesco Sabiu
Francesco Sabiu

Reputation: 11

Scala: "Expression doesn't conform to expected type"

I'm dealing with a simple Scala program in which I defined two auxiliary functions:

def getInt(number: String): Int ={
  if(number=="NULL")  0
  else number.toInt
}

def getFloat(number: String): Float ={
  if(number=="NULL") 0
  else number.toFloat
}

And a third recursive function that call them:

def foldr_rating_state(l: List[(String, String, String)], sum_sat:Int, n_sat:Int, sum_ret:Float, n_ret:Int) :Float = {
  match l{
    case Nil  => ((sum_sat/n_sat)/1600)*(1-(sum_ret/n_ret)).toFloat
    case x::xs    => {
      foldr_rating_state(xs.asInstanceOf[List[(String, String, String)]],
        sum_sat+getInt(x(1)),
        n_sat+(if (getInt(x(1))==0) 0 else getInt(x(1))),
        sum_ret+getFloat(x(2)),
        n_ret+(if (getFloat(x(2))==0.toFloat) 0 else getFloat(x(2))).toInt
      )
      0.toFloat
    }
    case _ => 0.toFloat
  }
}

But the compiler tells me that:

And IntelliJ says

Expression of type (String, String, String) doesn't conform to expected type Float

If I remove ".asInstanceOf[List[(String, String, String)]]" I get

Type mismatch, Expected List[(String, String, String)], Actual: List[Any]

Do you have any idea about the cause of these problems?

Thanks in advance!

Upvotes: 1

Views: 1923

Answers (2)

Sascha Kolberg
Sascha Kolberg

Reputation: 7152

You are accessing the fields of your tuples in a wrong way and the l blongs to the left of match. Try this 

def foldr_rating_state(l: List[(String, String, String)], sum_sat:Int, n_sat:Int, sum_ret:Float, n_ret:Int) :Float = {
  l match {
    case Nil  => 
      ((sum_sat/n_sat)/1600)*(1-(sum_ret/n_ret)).toFloat
    case x :: xs    => {
      foldr_rating_state(
        xs,
        sum_sat+getInt(x._1),
        n_sat+(if (getInt(x._1)==0) 0 else getInt(x._1)),
        sum_ret+getFloat(x._2),
        n_ret+(if (getFloat(x._2)==0.0f) 0 else getFloat(x._2).toInt
      )
    }
    case _ => 0.0f
  }
}

A word about getFloat(x._2)==0.0f: Comparing floating point types with ==may yield unexpected results due to a lack of precision.

Upvotes: 2

simpadjo
simpadjo

Reputation: 4017

1) Change match l to l match

2) Change x(1) to x._1 (x is a tuple, no a list)

Upvotes: 4

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