更新：我有一个大熊猫数据框，其中包含admitTime，dischargeTime，pat_name，pat_rec，它有大约500万条记录。我正在尝试根据其余列的dischargeTime datetime值来向前填充放电时间pat_name列，然后在此之后中断。
df：
admitTime dischargeTime pat_name pat_rec
2013-12-23 20:20:30 2013-12-23 21:12:00 Alex A4536
2013-12-23 21:00:30 2013-12-23 21:01:00 2013-12-23 21:01:30 2013-12-23 21:02:00 2013-12-23 21:02:30 2013-12-23 21:03:00 2013-12-23 21:03:30 2013-12-23 21:04:00 2013-12-23 21:04:30 2013-12-23 21:05:00 2013-12-23 21:05:30 2013-12-23 21:06:00 2013-12-23 21:06:30 2013-12-23 21:07:00 2013-12-23 21:07:30 2013-12-23 21:08:00 2013-12-23 21:08:30 2013-12-23 21:09:00 2013-12-23 21:09:30 2013-12-23 21:10:00 2013-12-23 21:10:30 2013-12-23 21:11:00 2013-12-23 21:11:30 2013-12-23 21:12:00 2013-12-23 21:12:30 2013-12-23 21:13:00 2013-12-23 21:13:30 2013-12-23 21:14:00 2013-12-21:18:00 Sam A4523 2013-12-23 21:14:30 2013-12-23 21:15:00 2013-12-23 21:15:30 2013-12-23 21:16:00 2013-12-23 21:16:30 2013-12-23 21:17:00 2013-12-23 21:17:30 2013-12-23 21:18:00 2013-12-23 21:18:30 2013-12-23 21:19:00 2013-12-23 21:19:30 2013-12-23 21:20:00
理想情况下，我希望我的df看起来像
datetime discchargeTime pat_name pat_rec
2013-12-23 20:20:30 2013-12-23 21:12:00 Alex A4536
2013-12-23 21:00:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:01:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:01:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:02:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:02:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:03:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:03:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:04:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:04:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:05:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:05:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:06:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:06:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:07:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:07:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:08:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:08:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:09:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:09:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:10:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:10:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:11:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:11:30 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:12:00 2013-12-23 21:12:00 Alex A4536 2013-12-23 21:12:30 2013-12-23 21:13:00 2013-12-23 21:13:30 2013-12-23 21:14:00 2013-12-21:18:00 Sam A4523 2013-12-23 21:14:30 2013-12-21:18:00 Sam A4523 2013-12-23 21:15:00 2013-12-21:18:00 Sam A4523 2013-12-23 21:15:30 2013-12-21:18:00 Sam A4523 2013-12-23 21:16:00 2013-12-21:18:00 Sam A4523 2013-12-23 21:16:30 2013-12-21:18:00 Sam A4523 2013-12-23 21:17:00 2013-12-21:18:00 Sam A4523 2013-12-23 21:17:30 2013-12-21:18:00 Sam A4523 2013-12-23 21:18:00 2013-12-21:18:00 Sam A4523 2013-12-23 21:18:30 2013-12-23 21:19:00 2013-12-23 21:19:30 2013-12-23 21:20:00
我曾尝试过，df[column_name].ffill()但后来意识到这样做不正确。
如果能得到任何建议，我将不胜感激。
您可以使用以下代码：
mask = df['admitTime'] > df['dischargeTime'].iloc[0] #masking where admit time is greater than discharge time
pd.concat([df[~mask].ffill(),df[mask]]) #ffill the remaining and concat with mask
admitTime dischargeTime pat_name pat_rec
0 2013-12-23 20:20:30 2013-12-23 21:12:00 Alex A4536
1 2013-12-23 21:00:30 2013-12-23 21:12:00 Alex A4536
2 2013-12-23 21:01:00 2013-12-23 21:12:00 Alex A4536
3 2013-12-23 21:01:30 2013-12-23 21:12:00 Alex A4536
4 2013-12-23 21:02:00 2013-12-23 21:12:00 Alex A4536
5 2013-12-23 21:02:30 2013-12-23 21:12:00 Alex A4536
6 2013-12-23 21:03:00 2013-12-23 21:12:00 Alex A4536
7 2013-12-23 21:03:30 2013-12-23 21:12:00 Alex A4536
8 2013-12-23 21:04:00 2013-12-23 21:12:00 Alex A4536
9 2013-12-23 21:04:30 2013-12-23 21:12:00 Alex A4536
10 2013-12-23 21:05:00 2013-12-23 21:12:00 Alex A4536
11 2013-12-23 21:05:30 2013-12-23 21:12:00 Alex A4536
12 2013-12-23 21:06:00 2013-12-23 21:12:00 Alex A4536
13 2013-12-23 21:06:30 2013-12-23 21:12:00 Alex A4536
14 2013-12-23 21:07:00 2013-12-23 21:12:00 Alex A4536
15 2013-12-23 21:07:30 2013-12-23 21:12:00 Alex A4536
16 2013-12-23 21:08:00 2013-12-23 21:12:00 Alex A4536
17 2013-12-23 21:08:30 2013-12-23 21:12:00 Alex A4536
18 2013-12-23 21:09:00 2013-12-23 21:12:00 Alex A4536
19 2013-12-23 21:09:30 2013-12-23 21:12:00 Alex A4536
20 2013-12-23 21:10:00 2013-12-23 21:12:00 Alex A4536
21 2013-12-23 21:10:30 2013-12-23 21:12:00 Alex A4536
22 2013-12-23 21:11:00 2013-12-23 21:12:00 Alex A4536
23 2013-12-23 21:11:30 2013-12-23 21:12:00 Alex A4536
24 2013-12-23 21:12:00 2013-12-23 21:12:00 Alex A4536
25 2013-12-23 21:12:30 NaT NaN NaN
26 2013-12-23 21:13:00 NaT NaN NaN
................
................
然后，您可以根据需要用空格替换nan。希望这可以帮助。
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