as.POSIXct with datetimes including midnight

Question

I am wanting to convert date-times stored as characters to date-time objects. However if a date time includes midnight then the resulting datetime object excludes the time component, which then throws an error when used in a later function (not needed here - but a function that extracts weather data for specified location and date-time).

Example code:

example.dates <- c("2011-11-02 00:31:00","2011-11-02 00:00:00","2011-11-02 00:20:22")
posix.dates   <- as.POSIXct(example.dates, tz="GMT", format="%Y-%m-%d %H:%M:%S")
posix.dates
posix.dates[2]

NB times is only excluded when the datetime containing midnight is called on it's own (atomic vector).

Is there a way of retaining the time data for midnight times? Can you suggest an alternative function?

Imf

The time information is there, it just is not displayed. I'm a bit surprised that this causes an error later on. Maybe the problem is with your later function. Could you show us that code? (As a proof that it is available see format(posix.dates, '%Y-%m-%d %M:%H') – Bastia

Thanks @Thilo. I am wanting to use the function 'NCEP.interp' in R package 'RNCEP'. Looking at the source code for that function, the error comes from the following line of code, which returns NA: strptime(posix.dates[2], "%Y-%m-%d %H:%M:%S",'UTC') This shouldn't be necessary considering that I am already using a datetime object, but that is how the function is written. – Imf

I fear your error is somewhere else. If I run strptime(posix.dates, "%Y-%m-%d %H:%M:%S",'UTC'), the results are fine and as expected. What is the actual error message? – Bastia

It's if you run it on the single value, not the whole vector: strptime(posix.dates[2], "%Y-%m-%d %H:%M:%S",'UTC') No error message there, but returns 'NA', which will give an error when used in later function. – Imf

I'd recommend against using strptime on POSIXct values. If you want to convert to POSIXlt, as.POSIXlt is better. If you want to use strptime, then first do the conversion to character yourself like this: strptime(format(posix.dates[2], "%Y-%m-%d %H:%M:%S"), "%Y-%m-%d %H:%M:%S", "UTC") – Distinctly

Answer 1

Okay, after some time I can reconfirm your problem.

For me this looks like a bug in R. I would suggest you to report it on https://bugs.r-project.org/bugzilla3/.

As a temporary workaround, you could try if it helps to overwrite the strptime function like this:

strptime <- function (x, format, tz = "") 
{
    if ("POSIXct" %in% class(x)) {
        x
    } else {
        y <- .Internal(strptime(as.character(x), format, tz))
        names(y$year) <- names(x)
        y
    }
}

Bastia

Thanks Thilo and @GSee. I can't rewrite the strptime or avoid using that unless I go into the package 'RNCEP' which calls the function - i.e. I'd have to rewrite the package source and recompile. For this specific case, running the 'NCEP.interp' function, the only easy work around I have thought of is not to convert the character datetime in the first place, and let the package do so with strptime - that seems to work. – Imf

Answer 2

Realise this is an old question now, but I had the same issue and found this solution:

https://mcmap.net/q/1719515/-r-lubridate-package-date-time-creation-omits-time-at-midnight

Essentially, all you need to do is apply formatting as follows. The OP's code needed to include the formatting call after the POSIXct function call.

posix.dates <- format(as.POSIXct(example.dates, tz="GMT"), format="%Y-%m-%d %H:%M:%S")

This worked for me.

Earpiercing

Answer 3

I prefer to use the lubridate package for date-times. It does not seem to cause problems here either:

example.dates <- c("2011-11-02 00:31:00","2011-11-02 00:00:00","2011-11-02 00:20:22")
library(lubridate)
ymd_hms(example.dates)

Kinzer

Thanks, but unfortunately that gives the same problem (see added two lines of code above). – Imf

doesnt solve this particular problem of needing the 00s displayed – Mandamandaean