[R] Query about use of format in strptime
David Winsemius
dwinsemius at comcast.net
Mon Apr 11 11:05:02 CEST 2016
> On Apr 11, 2016, at 1:48 AM, Stefano Sofia <stefano.sofia at regione.marche.it> wrote:
>
> Dear Jim and dear Enrico,
> thank you for your replies.
> Unfortunately your hints didn't solve my problem, and I am getting mad.
> Can I show you my whole process? I will be as quick as possible.
> I start from a data frame called Snow of the form
>
> year month day hh mm hs
> 2007 11 19 0 0 0.00
> 2007 11 19 0 30 0.00
> 2007 11 19 1 0 0.00
> 2007 11 19 1 30 0.00
> 2007 11 19 2 0 0.00
> 2007 11 19 2 30 0.00
> 2007 11 19 3 0 0.00
> 2007 11 19 3 30 0.00
> 2007 11 19 4 0 0.00
> 2007 11 19 4 30 0.00
> ...
>
> whth semi-hourly data.
> I need to deal with date so I used strptime:
>
> Snow$data_factor <- as.factor(paste(Snow$year, Snow$month, Snow$day, Snow$hh, Snow$mm, sep="-"))
> Snow$data_strptime <- strptime(Snow$data_factor, format = "%Y-%m-%d-%H-%M")
>
> It gives me
>
> year month day hh mm hs data_factor data_strptime
> 1 2007 11 19 0 0 0 2007-11-19-0-0 2007-11-19 00:00:00
> 2 2007 11 19 0 30 0 2007-11-19-0-30 2007-11-19 00:30:00
> 3 2007 11 19 1 0 0 2007-11-19-1-0 2007-11-19 01:00:00
> 4 2007 11 19 1 30 0 2007-11-19-1-30 2007-11-19 01:30:00
> 5 2007 11 19 2 0 0 2007-11-19-2-0 2007-11-19 02:00:00
> 6 2007 11 19 2 30 0 2007-11-19-2-30 2007-11-19 02:30:00
> 7 2007 11 19 3 0 0 2007-11-19-3-0 2007-11-19 03:00:00
> 8 2007 11 19 3 30 0 2007-11-19-3-30 2007-11-19 03:30:00
> 9 2007 11 19 4 0 0 2007-11-19-4-0 2007-11-19 04:00:00
> 10 2007 11 19 4 30 0 2007-11-19-4-30 2007-11-19 04:30:00
> ...
>
> The type of the column data_strptime is
> $data_strptime
> [1] "POSIXlt" "POSIXt"
>
> Because of some days (or part of them) might be missing, given a time interval I want to create a new data frame with all time-steps and then merge the new data frame with the old one.
> In order to create a new data frame with all time-steps, I thought to use
>
> df_new <- data.frame(data_strptime=seq(init_day, fin_day, by="30 mins"))
>
> and then
>
> Snow_all <- merge(df_new, Snow, by=("data_strptime"), all.x=TRUE)
>
> My problem is in dealing with and , respectively for example "200711190000" and "200711210000".
> I am not able to create a sequence of class "POSIXlt" "POSIXt", in order to merge the two data frames.
First you asked about character values with dashes in them and now you want no dashes. Make up our mind:
init_day="200711190000"
fin_day="200711210000".
df_new <- data.frame(data_strptime=seq(as.POSIXct(init_day, %Y%M%D%H%M"),
as.POSIXct(fin_day, %Y%M%D%H%M"), by="30 mins"))
Do NOT use POSIXlt for dataframe columns.
--
David.
>
> Could you please help me in this?
> Thank you again for your attention
> Stefano
>
>
> ________________________________________
> Da: Jim Lemon [drjimlemon at gmail.com]
> Inviato: lunedì 11 aprile 2016 9.47
> A: Stefano Sofia
> Cc: r-help at r-project.org
> Oggetto: Re: [R] Query about use of format in strptime
>
> Hi Stefano,
> As the help page says:
>
> "The default for the format methods is "%Y-%m-%d %H:%M:%S" if any
> element has a time component which is not midnight, and "%Y-%m-%d"
> otherwise. This is because when the result is printed, it uses the
> default format. If you want a specified output representation:
>
> format(strptime(init_day, format="%Y-%m-%d-%H-%M"),"%Y-%M-%d %H:%M")
> [1] "2015-30-24 00:30"
>
> For the "midnight" case:
>
> format(strptime(init_day, format="%Y-%m-%d-%H-%M"),"%Y-%m-%d %H:%M")
> [1] "2015-02-24 00:00"
>
> Jim
>
>
> On Mon, Apr 11, 2016 at 5:22 PM, Stefano Sofia
> <stefano.sofia at regione.marche.it> wrote:
>> Dear R-list users,
>> I need to use strptime because I have to deal with date with hours and minutes.
>> I read the manual for strptime and I also looked at many examples, but when I try to apply it to my code, I always encounter some problems.
>> I try to change the default format, with no success. Why? How can I change the format?
>>
>> 1.
>> init_day <- as.factor("2015-02-24-00-30")
>> strptime(init_day, format="%Y-%m-%d-%H-%M")
>> [1] "2015-02-24 00:30:00"
>> It works, but why also seconds are shown if in format seconds are not specified?
>>
>> 2.
>> init_day <- as.factor("2015-02-24-0-00")
>> strptime(init_day, format="%Y-%m-%d-%H-%M")
>> [1] "2015-02-24"
>> Again, the specified format is not applied. Why?
>>
>> Thank you for your attention and your help
>> Stefano
>>
>>
>> ________________________________
>>
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>> and provide commented, minimal, self-contained, reproducible code.
>
> ________________________________
>
> AVVISO IMPORTANTE: Questo messaggio di posta elettronica può contenere informazioni confidenziali, pertanto è destinato solo a persone autorizzate alla ricezione. I messaggi di posta elettronica per i client di Regione Marche possono contenere informazioni confidenziali e con privilegi legali. Se non si è il destinatario specificato, non leggere, copiare, inoltrare o archiviare questo messaggio. Se si è ricevuto questo messaggio per errore, inoltrarlo al mittente ed eliminarlo completamente dal sistema del proprio computer. Ai sensi dell’art. 6 della DGR n. 1394/2008 si segnala che, in caso di necessità ed urgenza, la risposta al presente messaggio di posta elettronica può essere visionata da persone estranee al destinatario.
> IMPORTANT NOTICE: This e-mail message is intended to be received only by persons entitled to receive the confidential information it may contain. E-mail messages to clients of Regione Marche may contain information that is confidential and legally privileged. Please do not read, copy, forward, or store this message unless you are an intended recipient of it. If you have received this message in error, please forward it to the sender and delete it completely from your computer system.
>
> ______________________________________________
> R-help at 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.
David Winsemius
Alameda, CA, USA
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