On Aug 2, 2011, at 7:55 AM, Liviu Andronic wrote:
Dear R developers
Would you consider adding a 'data.frame' method for the base::rep
function? The need to replicate a df row-wise can easily arise while
programming, and rep() is unable to handle such a case. See below.
x <- iris[1, ]
x[ rep(1,2), ] # "works"
I found a 'rep.data.frame' function in package 'mefa' [2], but I think
it would be nice to have it in base R. In any case, the code used by
the method is very simple.
require(mefa)
Loading required package: mefa
mefa 3.2-1 2011-05-13
mefa:::rep.data.frame
function (x, ...)
as.data.frame(lapply(x, rep, ...))
<environment: namespace:mefa>
And here's the example above:
rep(x, 2)
Sepal.Length Sepal.Width Petal.Length Petal.Width Species
1 5.1 3.5 1.4 0.2 setosa
2 5.1 3.5 1.4 0.2 setosa
I do not think the mefa 'rep.data.frame' code is a good example to
replicate ... as it were. It strips classes from any column that does
not have an associated 'rep' method, and the repetoire (we are in some
kind of self-referential loop here) of rep.* methods is pretty meager.
My initial thought was that the expected functionality would be found
with "[" using the template:
dfrm[rep(vec, times/each= vec2) , ]
It appears "[" proves would preserve classes for a much larger range.
methods("[")
> 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
# 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"
Since that works out of the box with fewer potential side-effects, I
am not sure a new method is needed.
--
David.
Please le t me know what you think. Regards
Liviu
[1] http://finzi.psych.upenn.edu/R/library/mefa/html/rep.data.frame.html
[2] http://cran.at.r-project.org/web/packages/mefa/index.html
--
David Winsemius, MD
West Hartford, CT
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