code: def slice(x, start, length):
      
      sc = SparkContext._active_spark_context
      return Column(sc._jvm.functions.slice(_to_java_column(x), start, length))
docs: Collection function: returns an array containing  all the elements in `x` from index `start`
      (or starting from the end if `start` is negative) with the specified `length`.
      >>> df = spark.createDataFrame([([1, 2, 3],), ([4, 5],)], ['x'])
      >>> df.select(slice(df.x, 2, 2).alias("sliced")).collect()
      [Row(sliced=[2, 3]), Row(sliced=[5])]