def getMatchingIDs(df : DataFrame): DataFrame = {
    //zwraca wiersze wyfiltrowane z df...
   }


    //definitely not scala way...
    var result : DataFrame = Seq.empty[(String,String)].toDF("col1", "col2")
    pairs.collect().foreach(row => {
       result = result.union(getMatchingIDs(df))
    }
    )

    result