From landronimirc at gmail.com  Wed Aug  3 08:45:47 2011
From: landronimirc at gmail.com (Liviu Andronic)
Date: Wed, 3 Aug 2011 08:45:47 +0200
Subject: [Rd] 'data.frame' method for base::rep()
In-Reply-To: <7EDF51C9-0E2A-47CA-81BF-3C73050D2B36@comcast.net>
References: <CABxs9VmouqjKpNvkzG5emHevXQtTRo9f81nxhOS9FvBo5V4maw@mail.gmail.com>
	<7EDF51C9-0E2A-47CA-81BF-3C73050D2B36@comcast.net>
Message-ID: <CABxs9VnmNAqDuBoGiH_CmznCpjceNJ+o9JN3eDg5bwO0xfAoyA@mail.gmail.com>

Hello David


On Tue, Aug 2, 2011 at 4:14 PM, David Winsemius <dwinsemius at comcast.net> wrote:
>> x <- data.frame(a = as.Date('2000-01-01'), b=as.Date('2001-01-01'))
>> x$d <- x$a -x$b
>> require(mefa)
>> rep(x, 2)
> ? ? ? ? ? a ? ? ? ? ?b ? ?d
> 1 2000-01-01 2001-01-01 -366
> 2 2000-01-01 2001-01-01 -366
>> str(rep(x,2))
> 'data.frame': ? 2 obs. of ?3 variables:
> ?$ a: Date, format: ?...
> ?$ b: Date, format: ?...
> ?$ d: num ?-366 -366 ? # notice that a difftime object has lost its class
>
Nice catch. Thanks for pointing it out.


> # Whereas using the [rep(. , .) , ] approach does preserve the difftime
> class.
>> str(x[rep(1,2) , ])
> 'data.frame': ? 2 obs. of ?3 variables:
> ?$ a: Date, format: ?...
> ?$ b: Date, format: ?...
> ?$ d:Class 'difftime' ?atomic [1:2] -366 -366 ? # leap year
> ?.. ..- attr(*, "units")= chr "days"
>
The above is nice. I wouldn't have thought of it.


> Since that works out of the box with fewer potential side-effects, I am not
> sure a new method is needed.
>
Your solution still seems more like an obscure side-effect of
subsetting than an intuitive feature, in the sense that before trying
it out the average user would probably first turn to base::rep() when
in need to replicate a df, and then (perhaps) to
mefa:::rep.data.frame() (with all the associated confusion and
pitfalls). I would tend to believe that if there is a clean R-ish way
to implement a base::rep.data.frame() it could still be useful.

Best regards
Liviu



[Rd] 'data.frame' method for base::rep()
Liviu Andronic