我面临的这个问题非常简单，但很奇怪，一直困扰着我。
我有一个数据框，如下所示：
df['datetime'] = df['datetime'].dt.tz_convert('US/Pacific')
df.head()
vehicle_id trip_id datetime
6760612 1000500 4f874888ce404720a203e36f1cf5b716 2017-01-01 10:00:00-08:00
6760613 1000500 4f874888ce404720a203e36f1cf5b716 2017-01-01 10:00:01-08:00
6760614 1000500 4f874888ce404720a203e36f1cf5b716 2017-01-01 10:00:02-08:00
6760615 1000500 4f874888ce404720a203e36f1cf5b716 2017-01-01 10:00:03-08:00
6760616 1000500 4f874888ce404720a203e36f1cf5b716 2017-01-01 10:00:04-08:00
我试图找出数据时间差异如下（以两种不同方式）：
df['datetime_diff'] = df['datetime'].diff()
df['time_diff'] = (df['datetime'] - df['datetime'].shift(1)).astype('timedelta64[s]')
对于特定的trip_id，我得到的结果如下：
df[trip_frame['trip_id'] == '4f874888ce404720a203e36f1cf5b716'][['datetime','datetime_diff','time_diff']].head()
datetime datetime_diff time_diff
6760612 2017-01-01 10:00:00-08:00 NaT NaN
6760613 2017-01-01 10:00:01-08:00 00:00:01 1.0
6760614 2017-01-01 10:00:02-08:00 00:00:01 1.0
6760615 2017-01-01 10:00:03-08:00 00:00:01 1.0
6760616 2017-01-01 10:00:04-08:00 00:00:01 1.0
但是对于像下面这样的其他trip_id，您可以观察到实际上我的datetime差为零（两个列都为零）。时差以秒为单位。
df[trip_frame['trip_id'] == '01b8a24510cd4e4684d67b96369286e0'][['datetime','datetime_diff','time_diff']].head(4)
datetime datetime_diff time_diff
3236107 2017-01-28 03:00:00-08:00 0 days 0.0
3236108 2017-01-28 03:00:01-08:00 0 days 0.0
3236109 2017-01-28 03:00:02-08:00 0 days 0.0
3236110 2017-01-28 03:00:03-08:00 0 days 0.0
df[df['trip_id'] == '01c2a70c25e5428bb33811ca5eb19270'][['datetime','datetime_diff','time_diff']].head(4)
datetime datetime_diff time_diff
8915474 2017-01-21 10:00:00-08:00 0 days 0.0
8915475 2017-01-21 10:00:01-08:00 0 days 0.0
8915476 2017-01-21 10:00:02-08:00 0 days 0.0
8915477 2017-01-21 10:00:03-08:00 0 days 0.0
任何人都知道真正的问题是什么？我将非常感谢。