Rounding errors in to_dataframe

The wfdb.Record.to_dataframe function generates a DataFrame from a Record object. The index of the resulting DataFrame is the elapsed or absolute time of each sample.

This code, however, will have significant rounding errors over a long record:

        if self.base_datetime is not None:
            index = pd.date_range(
                start=self.base_datetime,
                periods=self.sig_len,
                freq=pd.Timedelta(seconds=1 / self.fs),
            )
        else:
            index = pd.timedelta_range(
                start=pd.Timedelta(0),
                periods=self.sig_len,
                freq=pd.Timedelta(seconds=1 / self.fs),
            )

For example:

$ python3
>>> import wfdb
>>> r = wfdb.rdrecord('81739927', pn_dir='mimic4wdb/0.1.0/waves/p100/p10014354/81739927')
>>> str(r.base_datetime)
'2148-08-16 09:00:17.566000'
>>> r.fs
62.4725
>>> r.sig_len
6661120
>>> r.to_dataframe()
                             I     II    III      V  aVR     Pleth      Resp
2148-08-16 09:00:17.566000 NaN    NaN    NaN    NaN  NaN       NaN -0.751374
2148-08-16 09:00:17.582007 NaN    NaN    NaN    NaN  NaN       NaN -0.751374
2148-08-16 09:00:17.598014 NaN    NaN    NaN    NaN  NaN       NaN -0.751374
2148-08-16 09:00:17.614021 NaN    NaN    NaN    NaN  NaN       NaN -0.751374
2148-08-16 09:00:17.630028 NaN    NaN    NaN    NaN  NaN       NaN -0.751374
...                         ..    ...    ...    ...  ...       ...       ...
2148-08-17 14:37:22.033805 NaN -0.220 -0.285 -0.025  NaN  0.404297  0.487477
2148-08-17 14:37:22.049812 NaN -0.030  0.005  0.025  NaN  0.396484  0.530238
2148-08-17 14:37:22.065819 NaN -0.065 -0.030 -0.015  NaN  0.386475  0.574832
2148-08-17 14:37:22.081826 NaN -0.265 -0.255 -0.125  NaN  0.375977  0.621258
2148-08-17 14:37:22.097833 NaN -0.550 -0.610 -0.355  NaN  0.366211  0.664020

[6661120 rows x 7 columns]
>>> str(r.get_absolute_time(6661119)
'2148-08-17 14:37:22.384920'

$ wfdbtime -r mimic4wdb/0.1.0/waves/p100/p10014354/81739927/ s6661119
       s6661119    29:37:04.819 [14:37:22.385 17/08/2148]

Here, get_absolute_time is correct to the nearest microsecond and the wfdbtime command is correct to the nearest millisecond. to_dataframe, however, is off by 0.287 seconds.

I think this would be avoided by using start and end arguments to date_range or timedelta_range, rather than using start and freq.

wfdb.Record.to_dataframe 関数から始め、date_range または timedelta_range インデックスがサンプリング周波数からどのように構築されるかを調べてください。81739927 のような長いレコードについて、結果として得られる最終タイムスタンプを get_absolute_time および wfdbtime の出力と比較してください。完了の条件は、DataFrame インデックスが期待されるマイクロ秒またはミリ秒精度で正確な状態を保つことです。