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

[Jeff Newmiller]

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