r - converting dates using as.POSIXct

Question

I want to generate a vector of 21 years starting from 1990 to 2010. I am using the as.POSIXct function as follows

time=as.POSIXct("1990-01-01", tz="GMT")+0:20*3600*(24*365)

and i get the following answer

 [1] "1990-01-01 GMT" "1991-01-01 GMT" "1992-01-01 GMT" "1992-12-31 GMT" "1993-12-31 GMT" "1994-12-31 GMT"
 [7] "1995-12-31 GMT" "1996-12-30 GMT" "1997-12-30 GMT" "1998-12-30 GMT" "1999-12-30 GMT" "2000-12-29 GMT"
[13] "2001-12-29 GMT" "2002-12-29 GMT" "2003-12-29 GMT" "2004-12-28 GMT" "2005-12-28 GMT" "2006-12-28 GMT"
[19] "2007-12-28 GMT" "2008-12-27 GMT" "2009-12-27 GMT"

which ends in 2009 instead of 2010 as desired.

Can anyone help and if possible on how to generate years without the month and dates, only the years alone using as.POSIXct function?

Answer 1

Here is a solution that only requires you to specify the year range you want:

time <- as.POSIXct(paste0(1990:2010, "-01-01"), tz = "GMT")

I have assumed you want 1 January each year, not some close approximation.

Now if you only want to show the year you can do something like:

format(time, "%Y")
 #[1] "1990" "1991" "1992" "1993" "1994" "1995" "1996" "1997" "1998" "1999" "2000" "2001" "2002" "2003"
 #[15] "2004" "2005" "2006" "2007" "2008" "2009" "2010"