R-alpha: x[NA]

[Peter Dalgaard BSA]

Thomas Lumley <thomas@biostat.washington.edu> writes:

> That is, the presence of any NA would result in selecting only element
> as.numeric(T)==1.

Aha... Of course that only applies when you enter logical vectors
using c(...), if they result from a comparison, then the type would be
logical NA anyway. So the problem is that c(...) converts to numeric
if just one element is.numeric() even if that element is NA. Hmm. I
suppose that could be handled differently by having c() explicitly
ignoring NA when deciding on type, but that probably leads to more
problems elsewhere?

> BTW, while you obviously can't mix logical and numerical references I
> think it's unfortunate that you can't mix numeric and name-based
> references like
> R> names(x)<-letters[1:4]
> R> x
> a b c d 
> 1 2 3 4 
> R> x[c("a",2)]
> Error: subscript out of bounds
> 
> If you want a real example, suppose you had a model frame from which you
> wanted to extract the response (in position 1) and the variables whose
> names were in a vector nn
> 	mf[,c(1,nn)] 
> appears to be the obvious solution.

I think that the possibility of setting names(x)<-4:1 will demonstrate
why that can't work... Besides, can you be sure that the dependent
variable is the first one in a model frame any more?

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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