[R] Why is there error in as.POSIXlt.character when using strftime()?

[Jeff Newmiller]

strptime = string parse time (convert from string to POSIXlt, name of function as specified in POSIX standard)

strftime = string format time (make string, name of function as specified in POSIX standard)

as.POSIXlt = convert to POSIX list time format (same as strptime but name fits type conversion function naming pattern in R)

as.POSIXct = convert to POSIX continuous time (seconds since epoch, typically 1970-01-01 00:00:00 GMT, useful for computations)

?DateTimeClasses

On February 2, 2019 8:51:28 AM PST, C W <tmrsg11 using gmail.com> wrote:
>Thank you all very much, very helpful! :)
>
>I'm just curious, what does strptime(), strftime(), as.POSIXlt.(), and
>as.POSIXct() stand for?
>
>On Sat, Feb 2, 2019 at 10:41 AM Jeff Newmiller
><jdnewmil using dcn.davis.ca.us>
>wrote:
>
>> ... and in general, you need to specify the time zone to avoid
>surprises.
>> In many cases this can be as simple as
>>
>> Sys.setenv(TZ="GMT")
>>
>> but it can be specific to your data set also.
>>
>> On February 2, 2019 7:09:46 AM PST, Duncan Murdoch <
>> murdoch.duncan using gmail.com> wrote:
>> >On 01/02/2019 10:45 p.m., C W wrote:
>> >> Dear R community,
>> >>
>> >> I am working with dates. And I get the following error:
>> >>> strftime(dat[20], format="%H:%M")
>> >> Error in as.POSIXlt.character(as.character(x), ...) :
>> >>    character string is not in a standard unambiguous format
>> >
>> >You are using the wrong function:  strftime() formats a time object
>as
>> >a
>> >character string.  You want strptime() to convert character (or
>factor
>> >in your case) to a time object.
>> >
>> >But you need to give the format for the full string, not just the
>time
>> >at the end.
>> >
>> >If you really were intending to extract times from dat, then you
>need
>> >both conversions:
>> >
>> > > strftime(strptime(dat, format="%m/%d/%y %H:%M"), format =
>"%H:%M")
>> >  [1] "11:32" "11:42" "12:17" "12:31" "12:50" "14:10" "14:19"
>"14:59"
>> >"15:57" "16:00" "16:46" "16:51" "17:35" "17:59" "18:17" "19:07"
>"19:08"
>> >[18] "19:31" "21:21" "06:00" "06:20" "06:37" "06:40" "06:46" "07:20"
>> >"07:47" "07:50" "07:54" "08:11" "08:23" "08:31" "08:33" "08:43"
>"09:04"
>> >[35] "09:09" "09:30" "09:59" "10:01" "10:03" "10:05"
>> >
>> >Duncan Murdoch
>> >
>> >______________________________________________
>> >R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> >https://stat.ethz.ch/mailman/listinfo/r-help
>> >PLEASE do read the posting guide
>> >http://www.R-project.org/posting-guide.html
>> >and provide commented, minimal, self-contained, reproducible code.
>>
>> --
>> Sent from my phone. Please excuse my brevity.
>>

-- 
Sent from my phone. Please excuse my brevity.