What I want to do is sort List objects in Scala, not sort the elements in the list. For example If I have two lists of Ints:
val l1 = List(1, 2, 3, 7)
val l2 = List(1, 2, 3, 4, 10)
I want to be able to put them in order where l1 > l2.
I have created a case class that does what I need it to but the problem is that when I use it none of my other methods work. Do I need to implement all the other methods in the class i.e. flatten, sortWith etc.?
My class code looks like this:
class ItemSet(itemSet: List[Int]) extends Ordered[ItemSet] {
val iSet: List[Int] = itemSet
def compare(that: ItemSet) = {
val thisSize = this.iSet.size
val thatSize = that.iSet.size
val hint = List(thisSize, thatSize).min
var result = 0
var loop = 0
val ths = this.iSet.toArray
val tht = that.iSet.toArray
while (loop < hint && result == 0) {
result = ths(loop).compare(tht(loop))
loop += 1
}
if (loop == hint && result == 0 && thisSize != thatSize) {
thisSize.compare(thatSize)
} else
result
}
}
Now if I create an Array of ItemSets I can sort it:
val is1 = new ItemSet(List(1, 2, 5, 8))
val is2 = new ItemSet(List(1, 2, 5, 6))
val is3 = new ItemSet(List(1, 2, 3, 7, 10))
Array(is1, is2, is3).sorted.foreach(i => println(i.iSet))
scala> List(1, 2, 3, 7, 10)
List(1, 2, 5, 6)
List(1, 2, 5, 8)
The two methods that are giving me problems are:
def itemFrequencies(transDB: Array[ItemSet]): Map[Int, Int] = transDB.flatten.groupBy(x => x).mapValues(_.size)
The error I get is:
Expression of type Map[Nothing, Int] doesn't conform to expected type Map[Int, Int]
And for this one:
def sortListAscFreq(transDB: Array[ItemSet], itemFreq: Map[Int, Int]): Array[List[Int]] = {
for (l <- transDB) yield
l.sortWith(itemFreq(_) < itemFreq(_))
}
I get:
Cannot resolve symbol sortWith.
Is there a way I can just extend List[Int] so that I can sort a collection of lists without loosing the functionality of other methods?