[Solved]-explode a row of spark dataset into several rows with added column using flatmap-scala

Not tested but should work:

import spark.implicits._
import org.apache.spark.ml.linalg.Vector

df.as[(String, Vector)].flatMap { 
  case (j, ps) => ps.toArray.zipWithIndex.map { 
    case (p, ti) => JournalDis(j, ti, p)
  }
}