rounding times to the nearest hour in R

Question

I have data in the format

time <-  c("16:53", "10:57", "11:58")

etc

I would like to create a new column where each of these times is rounded to the nearest hour. I cannot seem to get the POSIX command to work for me.

as.character(format(data2$time, "%H:%M"))

Error in format.default(structure(as.character(x), names = names(x), dim = dim(x), : invalid 'trim' argument

Let alone use the round command. Can anyone advise?

`format` is used to go in the other direction (from a date-time to a particular representation). I'm not sure if there is a class for a partial date-time, e.g., only consisting of hours and minutes. — Frank, May 08 '13 at 15:23
http://stackoverflow.com/questions/16041093/round-a-posix-date-and-time-posixct-to-a-date-relative-to-a-timezone — Dieter Menne, May 08 '13 at 15:27
Something like: `as.POSIXlt(strptime(tt, format="%H:%M") + 30*60)$hour`?? — Arun, May 08 '13 at 15:29

score 23 · Accepted Answer · answered May 08 '13 at 16:15

23

## Example times
x <- c("16:53", "10:57", "11:58")

## POSIX*t objects need both date and time specified
## Here, the particular date doesn't matter -- just that there is one.
tt <- strptime(paste("2001-01-01", x), format="%Y-%m-%d %H:%M")

## Use round.Date to round, then format to format
format(round(tt, units="hours"), format="%H:%M")
# [1] "17:00" "11:00" "12:00"

answered May 08 '13 at 16:15

Josh O'Brien

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you don't really need to add a date, current date will be added automatically if you do `strptime(x, "%H:%M")` – eddi May 08 '13 at 16:33
2

@eddi -- Cool, but any chance that could get you in trouble for particular times on days with with a daylight savings time shift?? (I *said* the day didn't matter, but for this very reason chose one for which I don't think any place has a DLT shift...) – Josh O'Brien May 08 '13 at 16:36
Can't see why it would - and I did just check it and it works normally as far as I can tell. – eddi May 08 '13 at 16:44
2

@eddi If you're in the US, try setting your computer system date to March 10 2013 (the beginning of our DST this year), and then running `round(strptime("1:31", "%H:%M"), "hours")`. R returns `[1] "2013-03-10 03:00:00 PDT"` -- just what I was wanting to avoid. – Josh O'Brien May 08 '13 at 16:50
Thanks Josh! I see why I didn't see a difference before when testing, I was misformating the month by using %M instead of %m. You're right, adding a date is safer. – eddi May 08 '13 at 17:33
`round(...)` on a date. aweome - once again proving that we should always be thinking of dates as their underlying numerical structures. thanks @JoshO'Brien! – d8aninja Sep 19 '17 at 14:20

rounding times to the nearest hour in R

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