Converting numeric time to datetime POSIXct format in R

Question

I have a data frame containing what should be a datetime column that has been read into R. The time values are appearing as numeric time as seen in the below data example. I would like to convert these into datetime POSIXct or POSIXlt format, so that date and time can be viewed.

tdat <- c(974424L, 974430L, 974436L, 974442L, 974448L, 974454L, 974460L, 974466L, 974472L,
          974478L, 974484L, 974490L, 974496L, 974502L, 974508L, 974514L, 974520L, 974526L,
          974532L,974538L)

974424 should equate to 00:00:00 01/03/2011, but the do not know the origin time of the numeric values (i.e. 1970-01-01 used below does not work). I have tried using commands such as the below to achieve this and have spent time trying to get as.POXISct to work, but I haven’t found a solution (i.e. I either end up with a POSIXct object of NAs or end up with obscure datetime values).

Attempts to convert numeric time to datetime:

datetime <- as.POSIXct(strptime(time, format = "%d/%m/%Y %H:%M:%S"))
datetime <- as.POSIXct(as.numeric(time), origin='1970-01-01')

I am sure that this is a simple thing to do. Any help would be greatly received. Thanks!

Are these time values in hours, minutes or seconds? If you don't know the origin time, you have to know this in order to do the conversion. — Theodore Lytras
@ Theodore: they should be in hours. The datetime vales should run as so 00:00:00 01/03/2011, 06:00:00 01/03/2011, 12:00:00 01/03/2011, 18:00:00 01/03/2011, 00:00:00 02/03/2011 and so on (6-hour intervals). — jjulip

G. Grothendieck G. Grothendieck · Accepted Answer · 2014-07-01T11:31:56

Try one of these depending on which time zone you want:

t.gmt <- as.POSIXct(3600 * (tdat - 974424), origin = '2011-03-01', tz = "GMT") 

t.local <- as.POSIXct(format(t.gmt))

Converting numeric time to datetime POSIXct format in R

1 Answers