Iterate through List of case objects replace NaNs and write it back in Scala

Question

I have a List of case objects of which some values are NaN s and I have to replace them with 0.0 . So far I tried this code:

var systemInformation: List[SystemInformation] = (x.getIndividualSystemInformation)

systemInformation.foreach[SystemInformation] {
  _ match {
    case SystemInformation(a, b, c, d, e, f, g, h, i, j, k, l, m, x) if x.isNaN()
      => SystemInformation(a, b, c, d, e, f, g, h, i, j, k, l, m, 0.0)
    case SystemInformation(a, b, c, d, e, f, g, h, i, j, k, l, m, x) if !x.isNaN()
      => SystemInformation(a, b, c, d, e, f, g, h, i, j, k, l, m, x)
  }
}

But that does not write the changes back to systemInformation . So I added another List but got a type mismatch:

var systemInformation: List[SystemInformation] = (x.getIndividualSystemInformation)

var systemInformationWithoutNans: ListBuffer[SystemInformation] = new ListBuffer[SystemInformation]
systemInformation.foreach[SystemInformation] {
  _ match {
    case SystemInformation(a, b, c, d, e, f, g, h, i, j, k, l, m, x) if x.isNaN()
      => systemInformationWithoutNans += SystemInformation(a, b, c, d, e, f, g, h, i, j, k, l, m, 0.0)
    case SystemInformation(a, b, c, d, e, f, g, h, i, j, k, l, m, x) if !x.isNaN()
      => SystemInformation(a, b, c, d, e, f, g, h, i, j, k, l, m, x)
  }
}

The error occurs on the line with the += and is the following:

type mismatch;
found : scala.collection.mutable.ListBuffer[com.x.interfaces.SystemInformation]
required: com.x.interfaces.SystemInformation

Why does this not work? What would be a better way to replace the NaN s with 0.0 ?

Answer 1

Use map as bluenote10 sugested, but additionally, what about:

val transformedSystemInformation = systemInformation map (_ match {
    case s:SystemInformation if s.x.isNan() => s.copy(x = 0.0)
    case _ => _
})

Answer 2

You should use map instead of foreach .

Your first solution is basically the right way to go, but foreach only iterates over all elements, whereas map allows to map the elements from type A to B returning a new collection of type B .

Answer 3

Since your first question is not answered above, I thought I would add that this doesn't work, because the method +=

def +=(x: A): ListBuffer.this.type

returns a ListBuffer[SystemInformation] in this case, but you have parameterized foreach by the type SystemInformation

foreach[SystemInformation]

which is why the compiler is expecting the type SystemInformation rather than ListBuffer[SystemInformation] and returns the error

type mismatch;
found : scala.collection.mutable.ListBuffer[com.x.interfaces.SystemInformation]
required: com.x.interfaces.SystemInformation

If, on the other hand, you remove the type parameterization from foreach, your example will compile:

...
systemInformation.foreach { ... }
...

For a better approach, used Ian McMahon's suggested approach.