code: def round(col, scale=0):
      
      sc = SparkContext._active_spark_context
      return Column(sc._jvm.functions.round(_to_java_column(col), scale))
docs: Round the given value to `scale` decimal places using HALF_UP rounding mode if `scale` >= 0
      or at integral part when `scale` < 0.
  
      >>> spark.createDataFrame([(2.5,)], ['a']).select(round('a', 0).alias('r')).collect()
      [Row(r=3.0)]