As a practical matter, you can't treat POSIXlt as a list. The
documentation could be clearer about this. ?DateTimeClasses says
"Class ‘"POSIXlt"’ is a named list of vectors", and then later, "Note
that the internal list structure is somewhat hidden, as many methods
(including ‘length(x)’, ‘print()’ and ‘str’) apply to the abstract
date-time vector, as for ‘"POSIXct"’."
In other words, "POSIXct" is internally a list, but you can't really
treat it as one. If you want to access the internal list structure
directly, unclass it for first. For example:
> x = as.POSIXlt(Sys.time() - 1:20
>
> length(x)
[1] 20
> length(unclass(x))
[1] 11
> str(x)
POSIXlt[1:20], format: "2019-02-15 08:53:16" "2019-02-15 08:53:15"
"2019-02-15 08:53:14" ...
> str(unclass(x))
List of 11
$ sec : num [1:20] 16.9 15.9 14.9 13.9 12.9 ...
$ min : int [1:20] 53 53 53 53 53 53 53 53 53 53 ...
$ hour : int [1:20] 8 8 8 8 8 8 8 8 8 8 ...
$ mday : int [1:20] 15 15 15 15 15 15 15 15 15 15 ...
$ mon : int [1:20] 1 1 1 1 1 1 1 1 1 1 ...
$ year : int [1:20] 119 119 119 119 119 119 119 119 119 119 ...
$ wday : int [1:20] 5 5 5 5 5 5 5 5 5 5 ...
$ yday : int [1:20] 45 45 45 45 45 45 45 45 45 45 ...
$ isdst : int [1:20] 0 0 0 0 0 0 0 0 0 0 ...
$ zone : chr [1:20] "EST" "EST" "EST" "EST" ...
$ gmtoff: int [1:20] -18000 -18000 -18000 -18000 -18000 -18000 -18000
-18000 -18000 -18000 ...
- attr(*, "tzone")= chr [1:3] "" "EST" "EDT"
> sapply(x, length)
[1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
> sapply(unclass(x), length)
sec min hour mday mon year wday yday isdst zone gmtoff
20 20 20 20 20 20 20 20 20 20 20
Best,
Ista
On Fri, Feb 15, 2019 at 7:15 AM Newell, Paul
<paul.new...@metoffice.gov.uk> wrote:
>
> Many thanks Bill Dunlap.
>
> You are correct that `lapply` calls `as.list`, which I should have seen if I
> had looked a little harder.
>
> Whether that would have led me to locate `as.list.POSIXlt` is another matter.
>
> Best wishes.
>
>
>
> From: William Dunlap <wdun...@tibco.com>
> Sent: 14 February 2019 20:03
> To: Newell, Paul
> Cc: r-help@r-project.org
> Subject: Re: [R] POSIXlt class and lapply
>
> Somewhere between R-3.3.3 and R-3.5.2 a POSIXlt method for as.list() was
> added, and lapply probably calls as.list().
>
>
> > RCompare(methods("as.list"))
> R version 3.3.3 (2017-03-06) | R version 3.5.1
> (2018-07-02)
> [1] as.list.data.frame as.list.Date | [1] as.list.data.frame
> as.list.Date
> [3] as.list.default as.list.environment | [3] as.list.default
> as.list.environment
> [5] as.list.factor as.list.function | [5] as.list.factor
> as.list.function
> [7] as.list.numeric_version as.list.POSIXct | [7]
> as.list.numeric_version as.list.POSIXct
> see '?methods' for accessing help and source code | [9] as.list.POSIXlt
> | see '?methods' for
> accessing help and source code
>
>
>
>
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
>
>
>
> On Thu, Feb 14, 2019 at 9:45 AM Newell, Paul <paul.new...@metoffice.gov.uk>
> wrote:
>
> Dear R-helpers,
>
> We have recently upgraded from R-3.3.1 to R-3.5.2.
>
> It seems there has been a change in behaviour of `lapply` and the `POSIXlt`
> class that I cannot find explicitly documented.
>
>
> In R-3.3.1:
>
> > lapply(as.POSIXlt(Sys.Date()), length)
> $sec
> [1] 1
> $min
> [1] 1
> $hour
> [1] 1
> $mday
> [1] 1
> $mon
> [1] 1
> $year
> [1] 1
> $wday
> [1] 1
> $yday
> [1] 1
> $isdst
> [1] 1
>
>
> whereas, in R-3.5.2:
>
> > lapply(as.POSIXlt(Sys.Date()), length)
> [[1]]
> [1] 1
>
>
> Is this change in behaviour intentional?
>
> Realistically, I cannot see anything documented to say that `lapply` should
> behave as per R-3.3.1 on a `POSIXlt` object, so it is/was perhaps unwise to
> rely on it.
>
>
> Best wishes,
> Paul Newell
> ______________________________________________
> R-help@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.
>
> ______________________________________________
> R-help@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.
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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