Printing specific output in Scala

Question

I have the following array of arrays that represents a cycle in a graph that I want to print in the below format.

scala> result.collect

Array[Array[Long]] = Array(Array(0, 1, 4, 0), Array(1, 5, 2, 1), Array(1, 4, 0, 1), Array(2, 3, 5, 2), Array(2, 1, 5, 2), Array(3, 5, 2, 3), Array(4, 0, 1, 4), Array(5, 2, 3, 5), Array(5, 2, 1, 5))

0:0->1->4;
1:1->5->2;1->4->0;
2:2->3->5;2->1->5;
3:3->5->2;
4:4->0->1;
5:5->2->3;5->2->1;

How can I do this? I have tried to do a for loop with if statements like other coding languages but scala's ifs in for loops are for filtering and cannot make use if/else to account for two different criteria.

example python code

for (array,i) in enumerate(range(0,result.length)):
    if array[i] == array[i+1]:
        //print thing needed
    else:
       // print other thing

I also tried to do result.groupBy to make it easier to print but doing that ruins the arrays.

Array[(Long, Iterable[Array[Long]])] = Array((4,CompactBuffer([J@3677a08a)), (0,CompactBuffer([J@695fd7e)), (1,CompactBuffer([J@50b0f441, [J@142efc4d)), (3,CompactBuffer([J@1fd66db2)), (5,CompactBuffer([J@36811d3b, [J@61c4f556)), (2,CompactBuffer([J@2eba1b7, [J@2efcf7a5)))

Is there a way to nicely print the output needed in Scala?

Answer 1

This should do it:

result
  .groupBy(_.head)
  .toArray
  .sortBy(_._1)
  .map {
    case (node, cycles) =>
      val paths = cycles.map { cycle =>
        cycle
          .init // drop last node
          .mkString("->")
      }

      s"$node:${paths.mkString(";")}"
  }
  .mkString(";\n")

This is the output for the sample input you provided:

0:0->1->4;
1:1->5->2;1->4->0;
2:2->3->5;2->1->5;
3:3->5->2;
4:4->0->1;
5:5->2->3;5->2->1

Answer 2

It can be done without groupBy() and subsequent sorting. (Scala 2.13.x)

val collect: Array[Array[Long]] = ... //as posted

List.unfold(collect.map(_.init.mkString("","->",";"))){ ss =>
  Option.when(ss.nonEmpty){
    val (a,b) = ss.partition(_.startsWith(ss(0).take(1)))
    (s"${ss(0).take(1)}:${a.mkString}", b)
  }
}.foreach(println)