val columnName=Seq("col1","col2",....."coln");
dataframe.select("col1","col2"...)
columnName
dataframe.select()
val columnNames = Seq("col1","col2",....."coln")
// using the string column names:
val result = dataframe.select(columnNames.head, columnNames.tail: _*)
// or, equivalently, using Column objects:
val result = dataframe.select(columnNames.map(c => col(c)): _*)