On 15.09.2010 15:00, Seb wrote:
On Wed, 15 Sep 2010 11:29:23 +0200,
peter dalgaard<pda...@gmail.com> wrote:
On Sep 15, 2010, at 10:55 , Uwe Ligges wrote:
On 14.09.2010 20:50, Seb wrote:
On Tue, 14 Sep 2010 12:02:04 +0200,
Uwe Ligges<lig...@statistik.tu-dortmund.de> wrote:
It returns a list with athe class attribut set to "by", just use: x<-
by(.....) unclass(x)
Thanks Uwe, however, that still returns an array when using the
data.frame method for by():
R> class(unclass(with(warpbreaks, by(warpbreaks[, 1:2], tension, summary))))
[1] "array"
It seems as if the only way to really ensure a list:
R> class(lapply(unclass(with(warpbreaks, by(warpbreaks[, 1:2], tension,
summary))), function(x) x))
[1] "list"
but it seems like a waste to call another function just to do this.
Then you could still do
x<- by(.....)
attributes(x)<- NULL
Or just use c() instead of unclass(). (The root cause is that even with
simplify=FALSE, tapply() will always create an array, in this case a 1d array
with dim=3. The _contents_ of the array will be a list, though.)
Notice that in the relevant cases, what you get really _is_ a list, and both
walks and quacks like one. E.g.
L<- with(warpbreaks, by(warpbreaks[, 1], tension, mean, simplify=FALSE))
is.list(L)
[1] TRUE
L$M
[1] 26.38889
But if one tries to include this list dressed in 'by' clothes into an S4
class slot declared as a list, then we have problems. In that case, I
propose this simple patch to by.Rd, which simply removes the statement
about the result being *always* a list.
Index: by.Rd
===================================================================
--- by.Rd (revision 52375)
+++ by.Rd (working copy)
@@ -36,8 +36,6 @@
}
\value{
An object of class \code{"by"}, giving the results for each subset.
- This is always a list if \code{simplify} is false, otherwise a list or
- array (see \code{\link{tapply}}).
}
\seealso{\code{\link{tapply}}}
Thanks!
Why? It is still accessible as a list, even with S4 object, at least for
the cases I tried.
Uwe Ligges
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