Hi Simon, thank you for the concise reply.
Do you mean the reported behavior of drop() is not a bug?
It looks like a borderline bug to me (see below), but I'm not the judge of
that. If this is the intended behavior and serves an actual purpose, then
that could be explicitly documented in a \note{} on the help page.
Such a note would slightly reduce the surprise of users running into this
behavior.
This is related to the oddity that one-dimensional arrays are:
array(month.abb, dim=c(1,1,12)) # array
array(month.abb, dim=c(1,12)) # matrix
array(month.abb, dim=12) # array
Firstly, one would expect the pattern to be array-matrix-vector. Secondly,
it's easy to drop() the three-dimensional and two-dimensional objects, but
drop() does nothing to the one-dimensional array. Instead, it takes an
unintuitive combination of methods to convert a single-dimensional to a
vector, while retaining its names. Or I may well be missing something
obvious.
Best regards,
Arni
On Wed, 8 Sep 2010, Simon Urbanek wrote:
wrong address - did you mean R-devel?
Simon
On Sep 6, 2010, at 8:35 AM, Arni Magnusson wrote:
Bug or not, I was surprised by this behavior:
x <- tapply(chickwts$weight, chickwts$feed, median)
x # array ... I'd like to convert to vector with named elements
drop(x) # what, still an array?
drop(as.matrix(x)) # this works
drop(t(x)) # this works
I was expecting drop(x) to return a vector, and I suspect many R users
would too. The title in help(drop), "Drop Redundant Extent
Information", suggests that such a simple array would be converted to a
vector.
Reading through the help page, I note that this is perhaps not a clear
bug, but somewhat unclear behavior.
The most compact way to break the vector out of its eggshell seems to
be
t(x)[,]
but drop(x) would be much easier to read and write. There's nothing
particularly matrix about x, so it's not obvious that the conversion
should involve as.matrix(x).
Thanks,
Arni
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