我有以下数据集作为data.table(dt):
time wea
1 2016-06-16 00:04:50 cloudy
2 2016-06-16 02:14:55 cloudy
3 2016-06-16 03:19:04 cloudy
4 2016-06-16 04:19:24 cloudy
5 2016-06-16 05:23:45 cloudy
6 2016-06-16 06:25:05 cloudy
7 2016-06-16 07:26:46 cloudy
8 2016-06-16 08:27:06 cloudy
9 2016-06-16 09:34:09 sunny
10 2016-06-16 10:36:29 sunny
11 2016-06-16 11:39:09 sunny
12 2016-06-16 12:39:29 sunny
13 2016-06-16 13:44:50 rainy
14 2016-06-16 14:46:31 rainy
15 2016-06-16 15:47:12 rainy
16 2016-06-16 16:48:12 rainy
17 2016-06-16 17:49:54 sunny
18 2016-06-16 18:50:34 sunny
19 2016-06-16 19:51:34 cloudy
20 …