Converting numeric time to datetime POSIXct format in R

r datetime numeric posixct

27,886

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))

27,886

jjulip

Updated on July 02, 2020

Comments

jjulip almost 4 years
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!
- Theodore Lytras almost 10 years
  
  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.
- jjulip almost 10 years
  
  @ 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 almost 10 years

Thanks. The datetime vales should run from 00:00:00 01/03/2011 at 6-hour intervals i.e. 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. How would I adapt the code above to achieve this? Currently it gives the intervals in minutes rather than hours: i.e. "2011-01-03 00:00:00 GMT" "2011-01-03 00:00:06 GMT" "2011-01-03 00:00:12 GMT". Thanks!
Theodore Lytras almost 10 years

@jjulip If tdat is in 6 hour intervals, then in the first line just multiply tday-974424 by 60*6 to convert to minutes.
G. Grothendieck almost 10 years

@jjulip, See revised answer.
jjulip almost 10 years

@ Thank you both. Much appreciated. It worked using as.POSIXct((tdat - 974424)*3600, origin='2011-03-01', tz = "GMT").
Lazarus Thurston about 5 years

Surprising. My numeric values (for the year 2019) are coming in range of ~43,000. What could be the units of this?
Mark Neal almost 4 years

@Lazarus, days since 1/1/1900? Similar to Excel.