[R-sig-Geo] POSIX* objects and writeOGR()

[Michael Sumner]

POSIXlt stores the date-times as a list of vectors decomposed into the
(still numeric) component parts ("sec", "min", "hour", "mday", "mon",
"year", "wday", "yday", "isdst") so that cannot be stored as a single
column in the data frame - you would need 9 columns.


Compare these to see the underlying structure:

tm <- Sys.time()
## POSIXct
unclass(tm)
## POSIXlt
unclass(as.POSIXlt(tm))

You can just cast to character, directly or with format - see
?strptime for the full set of format tokens available. For example:

 as.character(tm)
##[1] "2009-12-31 07:28:01"
format(tm, "%Y/%b/%a %H:%M:%S")
##[1] "2009/Dec/Thu 07:28:01"

Hope that helps.

Regards, Mike.


On Thu, Dec 31, 2009 at 7:15 AM, Agustin Lobo <alobolistas at gmail.com> wrote:
> This might be a bit off-topic.
> I have to export as shape an Sp.Poly.DF in which
> one of the variables records date and time as POSIXtc. As
> writeOGR() complains about the POSIXct variable, I'm
> trying to convert to POSIXlt, which I think that will be
> accepted (another alternative would be coverting to an
> string char, but prefer to keep the SPDF object with
> a correct class definition for that variable).
> Let's call patata the table of the SPDF.
>
>> class(patata$Tima)
> [1] "POSIXt"  "POSIXct"
>
>> patata$Tima[1]
> [1] "2009-09-26 09:57:24 CEST"
>
>> as.POSIXlt(patata$Tima[1])
> [1] "2009-09-26 09:57:24 CEST"
>
>> class(as.POSIXlt(patata$Tima[1]))
> [1] "POSIXt"  "POSIXlt"
>
> So I was happy, but:
>
>> patata$Tima <- as.POSIXlt(patata$Tima)
> Error in `$<-.data.frame`(`*tmp*`, "Tima", value = list(sec = c(24, 33,  :
>  replacement has 9 rows, data has 44
> Calls: $<- -> $<-.data.frame
>
>
> Is there any way I can put the POSIXlt object in the table (patata) of the
> SPDF object?
>
> Thanks!
>
> Agus
>
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