Returns a DataFrame of observations, each containing a timestamp, a key, and a value.

        Parameters
        ----------
        sql_ctx : SQLContext
        ts_col : string
            The name for the timestamp column.
        key_col : string
            The name for the key column.
        val_col : string
            The name for the value column.

def to_observations_dataframe(self, sql_ctx, ts_col='timestamp', key_col='key', val_col='value'):
        """
        Returns a DataFrame of observations, each containing a timestamp, a key, and a value.

        Parameters
        ----------
        sql_ctx : SQLContext
        ts_col : string
            The name for the timestamp column.
        key_col : string
            The name for the key column.
        val_col : string
            The name for the value column.
        """
        ssql_ctx = sql_ctx._ssql_ctx
        jdf = self._jtsrdd.toObservationsDataFrame(ssql_ctx, ts_col, key_col, val_col)
        return DataFrame(jdf, sql_ctx)