One way, assuming your timestamps are POSIXct format:

truncInterval <- function ( x, dx=as.difftime(1,units="days") ) {
xn <- as.numeric( x )
result <- xn - xn %% as.numeric( dx, units="secs" )
class( result ) <- 'POSIXct'
result
}

truncInterval( as.POSIXct(c("2011-04-28 09:20:00", "2011-04-28 09:40:00")), as.difftime(30,units="mins") )

This may not work well if the timestamp granularity is more fine than one second.
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Schatzi <adele_thompson@cargill.com> wrote:

I have times and would like to round down to the earliest 30 minute increment. For instance, a time of 2011-04-28 09:02:00 (the as.numeric value = 1303999320) I would like it to be rounded down to: 2011-04-28 09:00:00 (the as.numeric value = 1303999200) Any ideas of how to do this? ----- In theory, practice and theory are the same. In practice, they are not - Albert Einstein -- View this message in context: http://r.789695.n4.nabble.com/Round-down-to-earliest-hour-or-half-hour-tp3509374p3509374.html Sent from the R help mailing list archive at Nabble.com._____________________________________________
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