How to fill a ListBuffer[ List[Any] ] (Scala)?

I have a ListBuffer declared like this:

var distances_buffer: ListBuffer[List[Any]] = ListBuffer.empty[List[Any]]

and I am trying to fill it with data like this:

for(current <- 0 to training_list_length - 1){
   //A and B are examples
   distances_buffer(current) ++= List[Any](A,B)
}

However I get the following error:

java.lang.IndexOutOfBoundsException: 0

What am I missing?

EDIT! More Info:

I have a list (Named: training_list) of points and their class. (x, y, class) :

training_list : List[((Double, Double, String))]

I also have an extra point with a x and a y value given.

My goal is to calculate the euclidean distance of the extra point from each point inside the training list, and create a result which look like this:

//example
List((x: Double, y: Double, class: String), distance: String)

List((4.3,3.0,Iris-setosa), 1.2529964086141665), (4.4,3.0,Iris-setosa), 1.341640786499874)...

As you can see, in the list I want to include the coordinates of the point (from the training_list), the class of the point and also the distance.

for(current <- 0 to training_list_length - 1){
    val dist = eDistance(test_x, test_y, training_x(current), training_y(current))
    distances_buffer += ListBuffer[Any](training_result(current),dist)
  }

After the creation of this list I want to sort it based on the distances. Also stuck here!

As suggested by Luis, Any and var are to be avoided if possible, so here is an example that might nudge you to consider a different approach

case class Point(x: Double, y: Double, `class`: String)

def distance(a: Point, b: Point): Double =
  math.hypot(a.x - b.x, a.y - b.y)

val targetPoint = Point(1,2,"Extra-point")
val training_list : List[((Double, Double, String))] = List((4.3,3.0,"Iris-setosa"), (4.4,3.0,"Iris-setosa"))
val points = training_list.map(Point.tupled)
val unsortedPoints: List[(Point, Double)] = points.map(point => (point, distance(point, targetPoint)))
unsortedPoints.sortBy(_._2)

which outputs

res0: List[(Point, Double)] = List((Point(4.3,3.0,Iris-setosa),3.4481879299133333), (Point(4.4,3.0,Iris-setosa),3.5440090293338704))

I have copied distance calculation from Xavier.