Dear r-users,

I have dailly rainfall data from year 1971 to 2000. I use aggregate to form monthly rainfall data.  What I don't understand is that the data for the year 2000 become on the top, instead of year 1971.  Here are some codes and output:


agg_dt1     <- aggregate(x=dt1[,4],by=dt1[,c(1,2)],FUN=sum)

> head(agg_dt1,20); tail(agg_dt1,20)
   Tahun Bulan     x
1      0     1 398.6
2     71     1 934.9
3     72     1 107.2
4     73     1 236.4
5     74     1  10.5
6     75     1 744.6
7     76     1   9.2
8     77     1 108.7
9     78     1 251.5
10    79     1 197.3
11    80     1 144.1
12    81     1 104.5
13    82     1  17.7
14    83     1 151.8
...

Thank you so much for your help.

Roslina
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