[R] convert S-Plus function to R function

[Roslina Zakaria]

Hi R-expert,
If I have this daily rainfall data, how do call a particular set of data?

Year,Month,Day,Amount
1981,1,1,0
1981,1,2,0
1981,1,3,78
1981,1,4,22
1981,1,5,2
1981,1,6,0
1981,1,7,0
1981,1,8,0
1981,1,9,0
1981,1,10,10
1981,1,11,0
1981,1,12,108
1981,1,13,328
1981,1,14,10
1981,1,15,0
1981,1,16,6
1981,1,17,0
1981,1,18,28
1981,1,19,0
1981,1,20,0
1981,1,21,0
1981,1,22,0
1981,1,23,0
1981,1,24,0
1981,1,25,32
1981,1,26,0
1981,1,27,2
1981,1,28,0
1981,1,29,2
1981,1,30,0
1981,1,31,0
1981,2,1,0
1981,2,2,118
1981,2,3,0
1981,2,4,0
1981,2,5,0
1981,2,6,12
1981,2,7,0
1981,2,8,0
1981,2,9,46
1981,2,10,4
1981,2,11,0
1981,2,12,0
1981,2,13,0
1981,2,14,0
1981,2,15,0
1981,2,16,0
1981,2,17,0
1981,2,18,0
1981,2,19,0
1981,2,20,0
1981,2,21,4
1981,2,22,16
1981,2,23,0
1981,2,24,0
1981,2,25,2
1981,2,26,0
1981,2,27,0
1981,2,28,0
1981,3,1,0
1981,3,2,0
1981,3,3,0
1981,3,4,0
1981,3,5,0
1981,3,6,0
1981,3,7,0
1981,3,8,0
1981,3,9,106
1981,3,10,10
1981,3,11,0
1981,3,12,0
1981,3,13,0
1981,3,14,0
1981,3,15,32
...
For example, if I would like to extract january and february data, and use 1/1/1901 as the origin. How do I use the dates function in R ? I did try to lookup in the manual, but not sure how to apply it?
This is my code in S-plus.
define.date1<-function(dt1,mt1,mt2,nn,da)
{  mt2<-mt2+1
   start<-julian(mt1, 1, nn, origin=c(month=1, day=1, year=1971))+1
   end<-julian(mt2, 1, nn, origin=c(month=1, day=1, year=1971))+da
   a<-dt1[start:end,]
   am<-as.matrix(a[,5])
}
Thank you so much for your kind attention and help.


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