我有一长串按以下方式构造的数据
Date, Time, Temperature, Moisture, Accumulated precipitation
1/01/2011, 00:00, 23, 50, 2,
1/01/2011, 00:15, 22, 45, 1,
1/01/2011, 00:30, 20, 39, 0,
1/01/2011, 01:00, 25, 34, 0,
1/01/2011, 01:15, 23, 50, 0,
.
.
.
.
1/01/2011, 23:45, 22, 40, 0,
.
.
.
.
31/01/2011, 00:00, 23, 45, 0,
如何获得变量的每日平均值Temperature
以及Moisture
每月第 31 天的平均值?