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

Also, I was able to extract date using
as.Date(dat, "%m/%d/%y")
[1] "2015-07-12" "2015-07-12" "2015-07-12" "2015-07-12" "2015-07-12"
 [6] "2015-07-12" "2015-07-12" "2015-07-12" "2015-07-12" "2015-07-12"
[11] "2015-07-12" "2015-07-12" "2015-07-12" "2015-07-12" "2015-07-12"
[16] "2015-07-12" "2015-07-12" "2015-07-12" "2015-07-12" "2015-07-13"
[21] "2015-07-13" "2015-07-13" "2015-07-13" "2015-07-13" "2015-07-13"
[26] "2015-07-13" "2015-07-13" "2015-07-13" "2015-07-13" "2015-07-13"
[31] "2015-07-13" "2015-07-13" "2015-07-13" "2015-07-13" "2015-07-13"
[36] "2015-07-13" "2015-07-13" "2015-07-13" "2015-07-13" "2015-07-13"
class(as.Date(dat, "%m/%d/%y"))
[1] "Date"
class(strftime(strptime(dat, format="%m/%d/%y %H:%M"), format =
"%m/%d/%y"))
[1] "character"

If I want to date caluculation, would as.Date() be more desirable? Or does
strftime() do the same thing?

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 at 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 at 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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Why is there error in as.POSIXlt.character when using strftime()?

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