as.POSIXct with datetimes including midnight

问题

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?

回答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
    }
}

回答2:

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)

回答3:

lubridate::as_datetime() is more flexible, accepting both dates (interpreted as 00:00:00) and datetimes.

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

ymd_hms(example.dates)
#> Warning: 1 failed to parse.
#> [1] NA                        "2011-11-02 00:31:00 UTC"
#> [3] "2011-11-02 00:00:00 UTC" "2011-11-02 00:20:22 UTC"

as_datetime(example.dates)
#> [1] "2011-11-02 00:00:00 UTC" "2011-11-02 00:31:00 UTC"
#> [3] "2011-11-02 00:00:00 UTC" "2011-11-02 00:20:22 UTC"

回答4:

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

https://stackoverflow.com/a/51195062/8158951

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.

来源：https://stackoverflow.com/questions/19756771/as-posixct-with-datetimes-including-midnight

标签

datetime

posixct