I have a question similar to Round a POSIX date (POSIXct) with base R functionality, but I'm hoping to always round the date up to midnight the next day (00:00:00).
Basically, I want a function equivalent to ceiling for POSIX-formatted dates. As with the related question, I'm writing my own package, and I already have several package dependencies so I don't want to add more. Is there a simple way to do this in base R?
Maybe
trunc(x,"days") + 60*60*24
> x <- as.POSIXct(Sys.time())
> x
[1] "2012-08-09 18:40:08 BST"
> trunc(x,"days")+ 60*60*24
[1] "2012-08-10 BST"
A quick and dirty method is to convert to a Date (which truncates the time), add 1 (which is a day for Date) and then convert back to POSIX to be at midnight UTC on the next day. As #Joshua Ulrich points out, timezone/daylight savings issues may give results you don't expect:
as.POSIXct(as.Date(Sys.time())+1)
[1] "2012-08-10 01:00:00 BST"
Related
I'm noticing this very confusing behavior.
library(lubridate)
x = as_date(-25567)
as.integer(as_datetime(x)) # Returns NA
How can I get this to return the seconds since (or in this case before) UNIX epoch?
This works with base R, now that we covered that you really want as.Date("1970-01-01").
R> as.POSIXct("1900-01-01 00:00:00")
[1] "1900-01-01 CST"
R> as.numeric(as.POSIXct("1900-01-01 00:00:00"))
[1] -2208967200
R>
I vaguely recall some OS-level irritations for dates prior to the epoch. This may fail for you on the world's most commonly used OS but that is not really R's fault...
I have a very specific problem. I have been trying to convert a date time character into a date time format in R. Example: "2017-05-21 00:00:00".
Whenever I try to convert it using strptime and as.POSIXct to a date time format it gives me "2017-05-21".
Thanks for any help
As #ngm says, this is only a formatting choice on the part of R. You can check to make sure it's actually midnight. Datetimes are stored as seconds past the epoch, and can actually be used in arithmetic.
t1 <- as.POSIXct("2017-05-21 00:00:00")
t1
# [1] "2017-05-21 EDT"
as.integer(t1)
# [1] 1495339200
So your time is 1,495,339,200 seconds after the epoch. Now we can look at midnight plus one second.
t2 <- as.POSIXct("2017-05-21 00:00:01")
t2
# [1] "2017-05-21 00:00:01 EDT"
as.integer(t2)
# [1] 1495339201
Which is one second higher than t1. So t1 is, in fact, midnight.
I want to convert number of days to date with time:
> 15525.1+as.Date("1970-01-01")
[1] "2012-07-04" ## correct but no time
I tried this:
> apollo.fmt <- "%B %d, %Y, %H:%M:%S"
> as.POSIXct((15525.1+as.Date("1970-01-01")), format=apollo.fmt, tz="UTC")
[1] "2012-07-04 04:24:00 CEST"
but as you see the results provide in CEST. But I need it it in UTC.
Any hints on this?
For the original conversion, refer to this question: Converting numeric time to datetime POSIXct format in R and these pages: Date-times in R , Date-time conversions and Converting excel dates (number) to R date-time object. Bascially, it depends on your data source, the time origin for that data sources (Excel, Apache etc.) and the units. For example, you may have the total time elapsed in seconds, minutes, hours or days since the time origin for your data source which will be different for Excel or Apache. Once you have this information, you can use strptime or origin arguments and convert to R date-time objects.
If you are only concerned with changing the timezone, you can use attr:
> u <- Sys.time()
> u
[1] "2017-12-21 09:01:35 EST"
> attr(u, "tzone") <- "UTC"
> u
[1] "2017-12-21 14:01:35 UTC"
You may want to check up on the valid timezones for your machine though. A good way to get a time-zone that works with your machine would be googleway::google_timezone. To get the coordinates for your location (or the location from where you're importing data), you can either look those up online or use ggmap::geocode() - useful if converting time stamps in data from different time zones.
I think the problem is as.POSIXct doesn't change anything if the time is already POSIXct, so the tz option has no effect.
Use attr as explained here
as.Date(date1) is incorrectly returning the previous day.
I suspect it has got to do with time zones, but I am still learning the very basics of R so I have little chance of solving it on my own.
The code I use to produce this is:
> a <- (capital_paid_summary_per_loan$Arrears_Date[1])
> a
[1] "2015-08-31 SAST"
> as.Date(a)
[1] "2015-08-30"
>
As you can see, the date starts off to be "2015-08-31" but as.Date() changes it to one day prior.
Any advice is welcome
If
date <- "2015-08-31 SAST"
You could use:
as.Date("2015-08-31 SAST",tz='SAST')
Which specifies the timezone as SAST, or you could use:
as.Date(gsub(' SAST','',date))
Which will remove the timezone from part of the string and then convert to date.
Lots of people ask how to strip the time and keep the date, but what about the other way around? Given:
myDateTime <- "11/02/2014 14:22:45"
I would like to see:
myTime
[1] "14:22:45"
Time zone not necessary.
I've already tried (from other answers)
as.POSIXct(substr(myDateTime, 12,19),format="%H:%M:%S")
[1] "2013-04-13 14:22:45 NZST"
The purpose is to analyse events recorded over several days by time of day only.
Thanks
Edit:
It turns out there's no pure "time" object, so every time must also have a date.
In the end I used
as.POSIXct(as.numeric(as.POSIXct(myDateTime)) %% 86400, origin = "2000-01-01")
rather than the character solution, because I need to do arithmetic on the results. This solution is similar to my original one, except that the date can be controlled consistently - "2000-01-01" in this case, whereas my attempt just used the current date at runtime.
I think you're looking for the format function.
(x <- strptime(myDateTime, format="%d/%m/%Y %H:%M:%S"))
#[1] "2014-02-11 14:22:45"
format(x, "%H:%M:%S")
#[1] "14:22:45"
That's character, not "time", but would work with something like aggregate if that's what you mean by "analyse events recorded over several days by time of day only."
If the time within a GMT day is useful for your problem, you can get this with %%, the remainder operator, taking the remainder modulo 86400 (the number of seconds in a day).
stamps <- c("2013-04-12 19:00:00", "2010-04-01 19:00:01", "2018-06-18 19:00:02")
as.numeric(as.POSIXct(stamps)) %% 86400
## [1] 0 1 2