How to define a list of lists in Scala?

Question

I would like to create a storage for the following type:

List(List(2.3,1.1),List(2.2, 1))

But if I do the following:

var y         


        

Answer 1

Couple of remarks:

F:\prog\scala\scala-2.8.0.r18341-b20090718020201\bin>scala
Welcome to Scala version 2.8.0.r18341-b20090718020201 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_13).
Type in expressions to have them evaluated.
Type :help for more information.

scala> var z = List(List (1.0, 2.2), List(2, 1.1, -2.1))
z: List[List[AnyVal]] = List(List(1.0, 2.2), List(2, 1.1, -2.1))

scala> var z = List(List (1.0f, 2.2f), List(2f, 1.1f, -2.1f))
z: List[List[Float]] = List(List(1.0, 2.2), List(2.0, 1.1, -2.1))

Meaning, like the question "Java: my method wants the double type instead of float?":

The 'f' at the end of the number makes it a float instead of a double.
Java won't automatically narrow a double to a float.

---

scala> var z = (1.0f :: 2.2f :: Nil) :: (2f :: 1.1f :: -2.1f :: Nil) :: Nil
z: List[List[Float]] = List(List(1.0, 2.2), List(2.0, 1.1, -2.1))

works too

---

Just adding the explicit type would not be enough:

scala> var z2 : List[List[Float]] = List(List(1.0, 2.2), List(2, 1.1, -2.1))
:4: error: type mismatch;
 found   : Double(1.0)
 required: Float
       var z2 : List[List[Float]] = List(List(1.0, 2.2), List(2, 1.1, -2.1))
                                              ^
:4: error: type mismatch;
 found   : Double(2.2)
 required: Float
       var z2 : List[List[Float]] = List(List(1.0, 2.2), List(2, 1.1, -2.1))
                                                   ^
:4: error: type mismatch;
 found   : Double(1.1)
 required: Float
       var z2 : List[List[Float]] = List(List(1.0, 2.2), List(2, 1.1, -2.1))
                                                                 ^
:4: error: type mismatch;
 found   : Double(-2.1)
 required: Float
       var z2 : List[List[Float]] = List(List(1.0, 2.2), List(2, 1.1, -2.1))
                                                                      ^

That is the same with one single variable:

scala> var f : Float = -2.1
:4: error: type mismatch;
 found   : Double(-2.1)
 required: Float
       var f : Float = -2.1
                       ^

scala> var f : Float = -2.1f
f: Float = -2.1