对于以下数据
> head(df)
Date Longitude Latitude Elevation Max.Temperature Min.Temperature Precipitation Wind Relative.Humidity Solar RO
1 2014-07-01 77.1875 7.96184 -9999 27.725 26.673 16.115560560 8.395378 0.8132272 23.08192 Yes
2 2014-07-02 77.1875 7.96184 -9999 27.931 26.897 0.700378560 8.062267 0.8074675 21.48473 Yes
3 2014-07-03 77.1875 7.96184 -9999 28.179 26.686 0.000000000 9.465022 0.8107901 24.14900 No
4 2014-07-04 77.1875 7.96184 -9999 27.657 26.545 0.003433226 9.397203 0.8195020 23.42036 Yes
5 2014-07-05 77.1875 7.96184 -9999 27.157 26.490 1.541518560 8.903047 0.8385059 23.90545 Yes
6 2014-07-06 77.1875 7.96184 -9999 27.308 …