[R] order list of date (bug?)

[William Dunlap]

It does look like "2016-03-27 02:35:00 CET" is a non-existent time
since the time sprang from 02:00-epsilon to 0:300 on that date.  The
POSIXlt entry for it is a missing value (per is.na()) and order() puts
missing values at the end, hence your problem.

It seems like a bug that POSIXlt entries with such invalid time print
oddly instead printing an NA.  is.na() says that they are
missing/invalid values.

> txt <- sprintf("2016-03-27 %02d:30:00", 1:4)
> txt
[1] "2016-03-27 01:30:00" "2016-03-27 02:30:00" "2016-03-27 03:30:00"
"2016-03-27 04:30:00"
> tim <- strptime(txt, format="%Y-%m-%d %H:%M:%S", tz="CET")
> tim
[1] "2016-03-27 01:30:00 CET"  "2016-03-27 02:30:00"      "2016-03-27
03:30:00 CEST" "2016-03-27 04:30:00 CEST"
> is.na(tim)
[1] FALSE  TRUE FALSE FALSE
> diff(tim)
Time differences in hours
[1] NA NA  1
> tim[3]-tim[1]
Time difference of 1 hours
> as.numeric(tim)
[1] 1459038600         NA 1459042200 1459045800

Bill Dunlap
TIBCO Software
wdunlap tibco.com


On Fri, Jan 20, 2017 at 9:10 PM, William Dunlap <wdunlap at tibco.com> wrote:
> When did the switch between 'summer time'/'winter time' (or 'daylight
> savings'/'standard') happen in CET last year?  (Did 2:35 exist on
> March 27, 2016?)
>
> At the R level, what is
>   as.numeric(strptime(df$DateTime, format='%Y-%m-%d %H:%M:%S'))
> with your time zone settings?
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
>
> On Thu, Jan 19, 2017 at 11:18 AM, rob vech <rob.vech87 at gmail.com> wrote:
>> Hi list,
>> I'd like to submit the following problem that seems a bug but it is so
>> strange that it could be my mind ... so
>> I would like to sort a list of date time items like in this script:
>>
>> df = data.frame(DateTime = c(
>> '2016-12-21 10:34:54',
>> '2016-12-21 11:04:54',
>> '2016-12-21 11:34:54',
>> '2016-03-27 02:05:50',
>> '2016-03-27 02:35:50',
>> '2016-12-21 12:04:54',
>> '2016-12-21 12:34:54'
>> ))
>>
>> df$DateTime = as.POSIXlt(strptime(df$DateTime, format='%Y-%m-%d %H:%M:%S'))
>>
>> ord = order(as.numeric(strptime(df$DateTime, format='%Y-%m-%d %H:%M:%S')))
>>
>> df.ord = df[ord,1]
>> df.ord
>>
>> I have the following results:
>>
>> "2016-12-21 10:34:54 CET"
>> "2016-12-21 11:04:54 CET"
>> "2016-12-21 11:34:54 CET"
>> "2016-12-21 12:04:54 CET"
>> "2016-12-21 12:34:54 CET"
>> "2016-03-27 02:05:50"
>> "2016-03-27 02:35:50"
>>
>> the last two terms should be before (note that CET is missing).
>>
>> if I change "2016-03-27 02:05:50" and "2016-03-27 02:35:50" to something
>> like "2016-03-27 01:05:50" and "2016-03-27 01:35:50"
>> it seems to work. It seems to have problem with 02 hours. Any ideas?
>> I'm using R-3.1.2 on Win
>> Thank you
>> rob
>>
>>         [[alternative HTML version deleted]]
>>
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