[R] POSIXlt class and lapply

[Newell, Paul]

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 <wdunlap using tibco.com>
Sent: 14 February 2019 20:03
To: Newell, Paul
Cc: r-help using 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.newell using 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
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