If you drop other columns (or map to a new df with only that column) and call collect i think you will get what you want.
Emm...I think you can do a df.map and store each column value to your list.
I am a new to Scala and Spark and trying to find relative API in DataFrame to solve my problem as title described. However, I just only find this API DataFrame.col(colName : String) : Column which returns an object of Column. Not the content. If only DataFrame support such API which like Column.toArray : Type is enough for me. But now, it doesn’t. How can I do can achieve this function ?