Adding Time to Posixct Object in R

Adding time to POSIXct object in R

POSIXct objects are a measure of seconds from an origin, usually the UNIX epoch (1st Jan 1970). Just add the requisite number of seconds to the object:

x <- Sys.time()
x
[1] "2012-08-12 13:33:13 BST"
x + 3*60*60 # add 3 hours
[1] "2012-08-12 16:33:13 BST"

How to add days to a POSIXct object in R

Your time format is not being tested by as.POSIXct. This is why you get this result.

You can use the following format to get it correct:

library(lubridate)

# note the format option to get it correct
input_time = as.POSIXct("2018-05-05T14:14:05", format = "%Y-%m-%dT%H:%M:%OS")
input_time + lubridate::days(1)

[1] "2018-05-06 14:14:05 UTC"

or just use everything with functions from lubridate:

input_time <- lubridate::ymd_hms("2018-05-05T14:14:05")
input_time + lubridate::days(1)

[1] "2018-05-06 14:14:05 UTC"

Adding time to time in R

When you use the format function, you create a character variable that cannot be sum. Therefore, I would suggest to keep then as POSIXt and use as character when necessary

Also, the minutes and hours functions from lubridate create a period object that is converted to a number when in a list (I don't completely understand this part here) and I could not sum using lists.

Anyways, if I understand propperly, I have manage to get the results you wanted by working with no list (you can put the results after on one, if you may) with the code:

hourTime<-(seq.POSIXt(as.POSIXct(Sys.Date()),
                         as.POSIXct(Sys.Date()+1),
                         by = "5 min"))

ARRIVALTIME <- sample(hourTime, 1000, replace=T)
TRETTIME <- ARRIVALTIME +
    (hours(sample(1:3, 1000, replace=T)) +
                     minutes(sample(1:60, 1000, replace=T)))

How to add/subtract time from a POSIXlt time while keeping its class in R?

Short answer: No

Long answer:

POSIXct and POSIXlt objects are two specific types of the more general POSIXt class (not in a strictly object oriented inheritance sense, but in a quasi-object oriented implementation sense). Code freely switches between these. When you add to a POSIXlt object, the actual function used is +.POSIXt, not one specifically for POSIXlt. Inside this function, the argument is converted into a POSIXct and then dealt with (added to).

Additionally, POSIXct is the number of seconds from a specific date and time. POSIXlt is a list of date parts (seconds, minutes, hours, day of month, month, year, day of week, day of year, DST info) so adding to that directly doesn't make any sense. Converting it to a number of seconds (POSIXct) and adding to that does make sense.

Modifying timezone of a POSIXct object without changing the display

EDITED:

My previous solution was passing a character value to origin (i.e.origin="1970-01-01"). That only worked here because of a bug (#PR14973) that has now been fixed in R-devel.

origin was being coerced to POSIXct using the tz argument of the as.POSIXct call, and not "GMT" as it was documented to do. The behavior has been changed to match the documentation which, in this case, means that you have to specify your timezone for both the origin and the as.POSIXct call.

datetime
#[1] "2011-01-01 12:32:23.233 GMT"
as.POSIXct(as.numeric(datetime), origin=as.POSIXct("1970-01-01", tz="Europe/Paris"),
           tz="Europe/Paris")
#[1] "2011-01-01 12:32:23.233 CET"

This will also works in older versions of R.

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