有一个样本数据集，包括每小时的风速和方向。
我想知道如何计算每日平均值。但我不知道。
请帮帮我。
V1 V2 V3
1 2015-07-15 0:00 0.3 296.9
2 2015-07-15 1:00 0.4 215.2
3 2015-07-15 2:00 0.4 204.8
4 2015-07-15 3:00 0.7 110.8
5 2015-07-15 4:00 0.4 287.6
6 2015-07-15 5:00 0.2 203.4
7 2015-07-15 6:00 0.1 253.1
8 2015-07-15 7:00 0.4 46.0
9 2015-07-15 8:00 0.5 298.8
10 2015-07-15 9:00 0.8 62.8
11 2015-07-15 10:00 0.9 183.4
12 2015-07-15 11:00 1.6 62.3
13 2015-07-15 12:00 2.8 44.3
14 2015-07-15 13:00 3.0 97.6
15 2015-07-15 14:00 3.3 78.6
16 2015-07-15 15:00 4.9 125.6
17 2015-07-15 16:00 4.9 116.9
18 2015-07-15 17:00 3.6 121.0
19 2015-07-15 18:00 1.8 111.2
20 2015-07-15 19:00 1.8 335.8
21 2015-07-15 20:00 1.5 287.4
22 2015-07-15 21:00 2.1 51.7
23 2015-07-15 22:00 0.4 232.6
24 2015-07-15 23:00 0.8 265.5
25 2015-07-16 0:00 0.2 269.7
26 2015-07-16 1:00 1.0 20.5
27 2015-07-16 2:00 2.4 17.0
28 2015-07-16 3:00 1.0 310.8
29 2015-07-16 4:00 0.7 63.8
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n sample