[R] empty data frame and POSIXct data types

Thu Jun 24 17:27:10 CEST 2021

Hello,

Inline.

Às 15:27 de 24/06/21, Stefano Sofia escreveu:
> Thank you Jeff and thank you Andrew
> 
> 1) Yes, I understand that it is a vector, even though is.vector(c(day1, day2)) is FALSE. Andrew explained to me why: it has attributes 'class' and 'tzone'.
> 2) I understand now that I created a data frame with only one row, and I am trying to fit a vector of length 2. I thought that, once created an empty data frame, 

But the data.frame is not empty, it has one row with perfectly valid NA's.

mydf
#  data_POSIX value
#1       <NA>    NA

You can rbind an empty df with another with the new values.

mydf2 <- data.frame()
mydf2
#data frame with 0 columns and 0 rows

rbind(mydf2, data.frame(data_POSIX = c(day1, day2), value = NA))
#  data_POSIX value
#1 2018-02-01    NA
#2 2018-02-02    NA

But once again assignment will fail, and for the same reason.

Hope this helps,

Rui Barradas

I could fit any vector without specifying the length since the beginning.
> 
> Now I will think about it.
> Thank you
> Stefano
> 
>           (oo)
> --oOO--( )--OOo--------------------------------------
> Stefano Sofia PhD
> Civil Protection - Marche Region - Italy
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> ________________________________________
> Da: Jeff Newmiller [jdnewmil using dcn.davis.ca.us]
> Inviato: giovedì 24 giugno 2021 15.46
> A: r-help using r-project.org; Stefano Sofia; r-help mailing list
> Oggetto: Re: [R] empty data frame and POSIXct data types
> 
> 1) It _is_ a vector. Why do you think it is not a vector?
> 
> 2) Your data frame has one row, with an NA in the date_POSIX column. You cannot fit a vector of length 2 as a column into a data frame with only 1 row.
> 
> What are you trying to do? Do you really want to end up with a 2-row data frame or a 3 row data frame?
> 
> On June 24, 2021 6:34:31 AM PDT, Stefano Sofia <stefano.sofia using regione.marche.it> wrote:
>> Dear R users,
>> I know that this question is silly (I am not a R newby) but I already
>> wasted quite a lot of energies trying to fill in an empty data frame
>> (with "POSIXct" "POSIXt" data type).
>>
>> Suppose I create
>> mydf <- data.frame(data_POSIX=as.POSIXct(NA), value=as.numeric(NA))
>> day1 <- as.POSIXct("2018-02-01-00-00", format="%Y-%m-%d-%H-%M",
>> tz="Etc/GMT-1")
>> day2 <- as.POSIXct("2018-02-02-00-00", format="%Y-%m-%d-%H-%M",
>> tz="Etc/GMT-1")
>>
>> then
>> mydf$data_POSIX <- c(day1, day2)
>>
>> does not work, it gives me:
>> "Error in `$<-.data.frame`(`*tmp*`, data_POSIX, value = c(1517439600,
>> 1517612400 :
>>   replacement has 2 rows, data has 1"
>>
>> There are few basic concepts that I am missing.
>> Why c(day1, day2) is not a vector?
>> Why I am not able to populate my data frame?
>>
>> Could somebody please give me the right hints?
>> Thank you for your precious help
>> Stefano
>>
>>
>>          (oo)
>> --oOO--( )--OOo--------------------------------------
>> Stefano Sofia PhD
>> Civil Protection - Marche Region - Italy
>> Meteo Section
>> Snow Section
>> Via del Colle Ameno 5
>> 60126 Torrette di Ancona, Ancona (AN)
>> Uff: +39 071 806 7743
>> E-mail: stefano.sofia using regione.marche.it
>> ---Oo---------oO----------------------------------------
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