hi jessica,

this should possibly do it...

year <- as.data.frame(c("2000-10-03","2000-10-03","2000-10-03","2000-10-03","2000-10-03","2000-10-03"
,"2000-10-03","2000-10-04","2000-10-04","2000-10-04"))
colnames(year) <- c("year")
time <- as.data.frame(c("14:00:00","14:10:00","14:20:00","15:30:00","16:40:00","16:50:00",
"17:00:00","17:10:00","17:20:00","18:30:00"))
colnames(time) <- c("time")

precipitation<-c(0,0.1,0,0,0,0,0.2,0.3,0.5,6)

DATA<-(cbind(year, time ,precipitation))

tapply(precipitation, year, sum)
tapply(precipitation, time, sum)

       
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