Question

I have two dates

begin <- as.Date("2007-05-20")
end   <- as.Date("2010-06-13")

How can I count the days per year?

The output should maybe look like this

year   days
2007   226
2008   366
2009   365
2010   164

Answer 1

Let’s first create a proper date sequence:

R> bd <- as.Date("2007-05-20")
R> ed <- as.Date("2010-06-13")
R> seqd <- seq(bd, ed, by="1 day")
R> head(seqd)
[1] "2007-05-20" "2007-05-21" "2007-05-22" "2007-05-23" "2007-05-24" "2007-05-25"

We then create a helper function which, given a date, returns its year:

R> getYear <- function(d) as.POSIXlt(d)$year + 1900
R> getYear(head(seqd))
[1] 2007 2007 2007 2007 2007 2007

After that, we just call table() on what the helper returns from the date sequence:

R> table(getYear(seqd))

2007 2008 2009 2010 
 226  366  365  164