From p.dalgaard at biostat.ku.dk  Wed Oct 22 23:03:40 2008
From: p.dalgaard at biostat.ku.dk (Peter Dalgaard)
Date: Wed, 22 Oct 2008 23:03:40 +0200
Subject: [Rd] R 2.8.0 qqnorm produces error with object of class zoo?
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Message-ID: <48FF952C.3040809@biostat.ku.dk>

Gabor Grothendieck wrote:
> And one other point.
> 
> z <- zoo(1:4)
> .gt(z, 1, 2)
> 
> fails because z[1] and z[2] are at different time points so
> 
>    z[1] == z[2]
> 
> is logical(0) because when zoo compares objects it aligns them
> first.

Yes, that was the point that I was trying to make. Well, arguably it 
doesn't "fail", it just does what it is supposed to do. Things would 
"work" with [[ or a preceding unclass(z), but that would break 
comparisons involving, say, POSIXlt objects. So you're sort of stuck 
between a rock and a hard place.

> 
> On Wed, Oct 22, 2008 at 2:19 PM, Gabor Grothendieck
> <ggrothendieck at gmail.com> wrote:
>> Yes, I noticed that but rank is not generic.  An xtfrm.zoo
>> method has been added to zoo on R-Forge but rank still
>> fails:
>>
>>> R.version.string
>> [1] "R version 2.8.0 Patched (2008-10-21 r46766)"
>>> packageDescription("zoo")$Version
>> [1] "1.5-3"
>>> library(zoo)
>>> # next line adds xtfrm zoo method
>>> xtfrm.zoo <- coredata
>>> z <- zoo(1:4)
>>> order(z) # ok
>> [1] 1 2 3 4
>>> qqnorm(z) # ok
>>> rank(z) # error
>> Error in if (xi == xj) 0L else if (xi > xj) 1L else -1L :
>>  argument is of length zero
>>
>>
>>>>> (If the MIME type is wrong, then that will happen.)
>>>>>
>>>>> Anyways, the root cause seems to be the new function .gt() which is
>>>>> related to
>>>>>
>>>>>    o   New generic function xtfrm() as an auxiliary helper for
>>>>>        sort(), order() and rank().  This should return a numeric
>>>>>        vector that sorts in the same way as its input.  The default
>>>>>        method supports any class with ==, > and is.na() methods but
>>>>>        specific methods can be much faster.
>>>>>
>>>>>        As a side-effect, rank() will now work better on classed
>>>>>        objects, although possibly rather slowly.
>>>>>
>>>>> Here, "better" may be in the eyes of the beholder, for
>>>>>
>>>>>
>>>>>> dax[3]==dax[6]
>>>>>>
>>>>> Data:
>>>>> logical(0)
>>>>>
>>>>> Index:
>>>>> integer(0)
>>>>>
>>>>> and accordingly
>>>>>
>>>>>
>>>>>> rank(dax)
>>>>>>
>>>>> Error in if (xi == xj) 0L else if (xi > xj) 1L else -1L :
>>>>>  argument is of length zero
>>>>>
>>>>> which is the error that you are seeing.
>>>>>
>>>>> What to do about it is a bit dubious. Obviously, we don't want to "fix"
>>>>> .gt() so that it automatically unclasses objects, and I assume that zoo
>>>>> has its reasons for not wanting to compare series with different
>>>>> indices. So I suppose that either the user must unclass, or zoo define
>>>>> rank.zoo.
>>>>>
>>>> Actually qqnorm does not use rank but it does use order and with the
>>>> xtfrm.zoo method I mentioned qqnorm works with zoo; however, I think
>>>> rank needs to be fixed in R to make use of xtfrm as well since I would have
>>>> expected that supplying an xtfrm method for zoo would be sufficient to
>>>> get both order and rank to work without giving errors.  Also note that rank
>>>> is not generic.
>>>>
>>> Notice that xtfrm.default() uses rank()....
>>>
>>> --
>>>   O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
>>>  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
>>>  (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
>>> ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907
>>>
>>>
>>>


-- 
    O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
  (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907



[Rd] R 2.8.0 qqnorm produces error with object of class zoo?
Peter Dalgaard