code: def substring_index(str, delim, count):
      
      sc = SparkContext._active_spark_context
      return Column(sc._jvm.functions.substring_index(_to_java_column(str), delim, count))
docs: Returns the substring from string str before count occurrences of the delimiter delim.
      If count is positive, everything the left of the final delimiter (counting from left) is
      returned. If count is negative, every to the right of the final delimiter (counting from the
      right) is returned. substring_index performs a case-sensitive match when searching for delim.
  
      >>> df = spark.createDataFrame([('a.b.c.d',)], ['s'])
      >>> df.select(substring_index(df.s, '.', 2).alias('s')).collect()
      [Row(s=u'a.b')]
      >>> df.select(substring_index(df.s, '.', -3).alias('s')).collect()
      [Row(s=u'b.c.d')]