[R] seq curiosity

[Peter Dalgaard BSA]

Uwe Ligges <ligges at statistik.uni-dortmund.de> writes:

> John Aitchison wrote:
> > 
> > Is this a bug or a feature?
> > 
> > > seq(0:4)  # colon
> > [1] 1 2 3 4 5
> > > 0:4
> > [1] 0 1 2 3 4
> > > seq(0,4)
> > [1] 0 1 2 3 4
> > 
> > I am aware that the first usage is incorrect, but I was surprised that
> > I did not get any sort of syntax error
> 
> It's a feature! It's mentioned in the help page. If you provide a vector
> (length > 1) as an argument to seq(), seq() is smart enough to detect
> the case "seq(along)":
> 
>  along <- 0:4
>  seq(along)
> 
> The same should happen for
> 
>  along <- LETTERS[10:14]
>  along
>  seq(along)
> 
> Everything works perfectly!

Well, almost. The case where x is numeric and length(x) == 1 is the
source of some subtle and nasty bugs. Try a couple of iterations of

 x <- rnorm(20, sd=100) ; seq(x[x>100]) 

and you'll see the problem.

However, we probably have to retain it for compatibility.

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