Check groups overlap

group-overlap-detection.scala

// Data example:
// id    group
// 1     A
// 2     A
// 2     B
// In this case object `2` belongs to both groups "A" and "B"
val overlappedGroups = groups.select($"id", $"group" as "_group")

groups
    .join(overlappedGroups, (groups("id") === overlappedGroups("id")) && ($"group" < $"_group"))  // NOTE: group A < group B, so duplicates (A,B) (B,A) would be removed.
    .groupBy("group", "_group")
    .count()
    .show()