code: def _create_function_over_column(name, doc=""):
      
      def _(col):
          sc = SparkContext._active_spark_context
          jc = getattr(sc._jvm.functions, name)(_to_java_column(col))
          return Column(jc)
      _.__name__ = name
      _.__doc__ = doc
      return _
docs: Similar with `_create_function` but creates a PySpark function that takes a column
      (as string as well). This is mainly for PySpark functions to take strings as
      column names.