Filter dataframe on non-empty WrappedArray

I don't think you need to use a UDF here.

You can just use size method and filter all those rows with array size = 0

df.filter(""" size(fahrspur_liste) != 0 """)

You can do this with an udf in Spark:

val removeEmpty = udf((array: Seq[Long]) => !array.isEmpty)

val df2 = df.filter(removeEmpty($"fahrspur_liste"))

Here the udf checks if the array is empty or not. The filter function will then remove those that come back as true.