python - 在特定时间范围内选择观察 datetime64[ns] 类型

Question

我有一个 pandas dataframe(dfnew)，其中一列 (timestamp) 是 datetime64[ns] 类型。现在我想看看有多少观测值在特定时间范围内，比如说 10:00:00 到 12:00:00。

    dfnew['timestamp'] = dfnew['timestamp'].astype('datetime64[ns]')
    dfnew['timestamp]
0    2013-12-19 09:03:21.223000
1    2013-12-19 11:34:23.037000
2    2013-12-19 11:34:23.050000
3    2013-12-19 11:34:23.067000
4    2013-12-19 11:34:23.067000
5    2013-12-19 11:34:23.067000
6    2013-12-19 11:34:23.067000
7    2013-12-19 11:34:23.067000
8    2013-12-19 11:34:23.067000
9    2013-12-19 11:34:23.080000
10   2013-12-19 11:34:23.080000
11   2013-12-19 11:34:23.080000
12   2013-12-19 11:34:23.080000
13   2013-12-19 11:34:23.080000
14   2013-12-19 11:34:23.080000
15   2013-12-19 11:34:23.097000
16   2013-12-19 11:34:23.097000
17   2013-12-19 11:34:23.097000
18   2013-12-19 11:34:23.097000
19   2013-12-19 11:34:23.097000
Name: timestamp

    dfnew['Time']=dfnew['timestamp'].map(Timestamp.time)
    t1 = datetime.time(10, 0, 0)
    t2 = datetime.time(12, 0, 0)
    print len(dfnew[t1<dfnew["Time"]<t2])

这会产生错误 TypeError: can't compare datetime.time to Series.我是 Pandas 数据框的新手。我想我在这里犯了一个非常愚蠢的错误。感谢任何帮助。

Answer 1

您可以使用 DatetimeIndex indexer_between_time方法，所以这里使用它的一个技巧是将系列/列传递给 DatetimeIndex 构造函数:

from datetime import time

# s is your datetime64 column

In [11]: pd.DatetimeIndex(s).indexer_between_time(time(10), time(12))
Out[11]: 
array([ 1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19])

这里获取的是10到12(含*)之间的时间位置，所以用iloc来过滤:

In [12]: s.iloc[pd.DatetimeIndex(s).indexer_between_time(time(10), time(12))]
Out[12]: 
1    2013-12-19 11:34:23.037000
2    2013-12-19 11:34:23.050000
3    2013-12-19 11:34:23.067000
4    2013-12-19 11:34:23.067000
5    2013-12-19 11:34:23.067000
6    2013-12-19 11:34:23.067000
7    2013-12-19 11:34:23.067000
8    2013-12-19 11:34:23.067000
9    2013-12-19 11:34:23.080000
10   2013-12-19 11:34:23.080000
11   2013-12-19 11:34:23.080000
12   2013-12-19 11:34:23.080000
13   2013-12-19 11:34:23.080000
14   2013-12-19 11:34:23.080000
15   2013-12-19 11:34:23.097000
16   2013-12-19 11:34:23.097000
17   2013-12-19 11:34:23.097000
18   2013-12-19 11:34:23.097000
19   2013-12-19 11:34:23.097000
Name: timestamp, dtype: datetime64[ns]

* include_start 和 include_end 是 indexer_between_time 的可选 bool 参数。