Convert Day of Year to Datetime

Hi Everyone,

I'm currently trying to convert a day of the year (DOY) value with decimals to datetimes. What I mean by this for example, the value 32.5 represents the date Feburary 1st, 12pm UTC. I've looked all over and I can't seem to find anything to convert this properly. Any suggestions would be great.

An example dataframe for code

df<-data.frame("DOY" = c(32.5, 33, 33.5), "Value" = c(5,10,7))

How about this?

# 1.4 days into the year
secs_per_day <- 24*3600
as.POSIXct(1.4*secs_per_day,tz="GMT",origin="2019-12-31")
[1] "2020-01-01 09:36:00 GMT"
1 Like

Here is a similar approach using lubridate functions. If you want 1.0 to mean Jan 01 00:00:00, then I guess you have to subtract 1 from the day-of the-year value.

DATE <- ymd_hms("2020-01-01 00:00:00")
DATE %m+% seconds_to_period(32.5*86400)
[1] "2020-02-02 12:00:00 UTC"
1 Like

This is also a great solution (I do like to use lubridate whenever possible). I also found that using the other solution above and setting the origin to one day earlier also solves the issue of making January 1st the first day.

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This is exactly what I'm looking for. Thank you!