val categoryMap = mutable.Map.empty[Int, mutable.Map[String, IndexedSeq[String]]]
val namesCategories = IndexedSeq.newBuilder[String]
...
myIterator.foreach{ t=>
      ...
      if(!(categoryMap.contains(iLevel))) {
        categoryMap.put(iLevel, mutable.Map.empty[String, IndexedSeq[String]])
      }
      categoryMap(iLevel).put(catCode, namesCategories)
    }