问题
For logging purposes, how can an R script get the current date and time, in the UTC time zone, as an ISO 8601 string in this format:
2015-12-31T14:26:56.600374+00:00
as.POSIXlt seems to be the solution, and the documentation claims that it accepts a format parameter, but I can't make that work (on R version 3.1.3):
> as.POSIXlt(Sys.time(), "UTC", "%Y-%m-%dT%H:%M:%S")
[1] "2015-04-08 14:37:58 UTC"
> as.POSIXlt(Sys.time(), tz="UTC", format="%Y-%m-%dT%H:%M:%S")
[1] "2015-04-08 14:38:02 UTC"
> as.POSIXct(Sys.time(), tz="UTC", format="%Y-%m-%dT%H:%M:%S")
[1] "2015-04-08 11:38:22 BRT"
回答1:
as.POSIXlt (and as.POSIXct) are for input. Use either format or strftime for output. See ?strftime for details on format strings:
tm <- as.POSIXlt(Sys.time(), "UTC", "%Y-%m-%dT%H:%M:%S")
strftime(tm , "%Y-%m-%dT%H:%M:%S%z")
#[1] "2015-04-08T15:11:22+0000"
I don't think that the colon in the timezone output is requirement of the ISO 8601 format but I could be wrong on that point. The help page says the standard is POSIX 1003.1. May need to put in the colon with a regex substitution if needed.
After looking at http://dotat.at/tmp/ISO_8601-2004_E.pdf I see that there is no colon in the "basic" format" timezone representation, but there is one in the "extended format".
回答2:
The package parsedate recognizes and parses Dates in various formats, including all ISO 8601 Formats:
format_iso_8601(Sys.time())
# [1] "2017-09-01T10:59:22+00:00"
来源：https://stackoverflow.com/questions/29517896/current-time-in-iso-8601-format