On Fri, Jun 12, 2009 at 6:09 AM, Duncan Murdoch <murd...@stats.uwo.ca>wrote:
> On 11/06/2009 5:35 PM, Stavros Macrakis wrote:
>
>> A table without names displays like a vector:
>>
>> > unname(table(2:3))
>> [1] 1 1 1
>>
>> and preserves the table class (as with unname in general):
>>
>> > dput(unname(table(2:3)))
>> structure(c(1L, 1L), .Dim = 2L, class = "table")
>>
>> Does that make sense? R is not consistent in its treatment of such
>> unname'd
>> tables:
>>
>
> One of the complaints about the S3 object system is that anything can claim
> to be of class "foo", even if it doesn't have the right structure so that
> foo methods work for it.
Yes, that is one of its flaws. More specifically, in this case, operations
on S3 objects can change them from being valid to being invalid.
> I think that's all you're seeing here: you've got something that is
> mislabelled as being of class "table".
Yes.
> The solution is "don't do that".
Agreed! But it's not clear to me how unname can *know* how not to do that
in the general case. After all, unname on a vector of POSIXct's leaves a
valid POSIXct object.
...
>> PS What is the standard way of extracting just the underlying vector?
>> c(unname(...)) works -- is that what is recommended?
>>
>
> I would use as.numeric(), but I don't claim it's standard.
>
Makes sense, as does the suggestion as.vector. So I guess the summary of
'stripping' operations is:
c --- strip all attributes (including most but not all classes) except for
names
unname -- strip name attributes, but no other attributes (including class)
unclass -- strip only class attribute
as.vector -- strip all attributes including class and name; convert generic
vectors to atomic vectors
Am I missing others?
-s
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