def to_dataframe(self):
return pd.DataFrame.from_records(list(self.data),<EOL>columns=['<STR_LIT:time>', '<STR_LIT>',<EOL>'<STR_LIT:value>', '<STR_LIT>'])<EOL>
Convert this annotation to a pandas dataframe.

        Returns
        -------
        df : pd.DataFrame
            Columns are `time, duration, value, confidence`.
            Each row is an observation, and rows are sorted by
            ascending `time`.