numeric(0) -> NA

[Peter Dalgaard BSA]

Bill Simpson <wsimpson@uwinnipeg.ca> writes:

> I noticed this in current intermediate patch version:
> > runif(0,0,4095)
> numeric(0)
> > round(runif(0,0,4095))
> [1] NA
> 
> I don't like it, but maybe it is the way it is supposed to be. I would
> prefer for it to stay numeric(0).
> 
> I notice also
> > ceiling(runif(0,0,4095))
> numeric(0)
> > floor(runif(0,0,4095))
> numeric(0)
> which leads me to thing round() is not working right.

You're right, but it's not all that easily fixed. The problem is that
round() unlike the other two isn't a unary operation (it has a digits
argument) and the automatic logic for binary functions is that 
length(f(a,b)) = max(length(a),length(b)).

There are several of these anomalies, e.g.:

> log(numeric(0))
numeric(0)
> log(numeric(0),10)
[1] NA
> log10(numeric(0))
[1] NA
> pt(numeric(0),15)
[1] NA
> choose(numeric(0),5)
[1] NA

whereas Splus has

> log(numeric(0))
numeric(0)
> log(numeric(0),10)
[1] NA
> log10(numeric(0))
[1] NA
> pt(numeric(0),15)
numeric(0)
# choose doesn't exist...
>  round(numeric(0))
numeric(0)

I.e. it seems to special-case *some* functions....

We probably should have a special version of math2() which said that
the first argument was more important than the other.

> BTW I think it is a ghastly waste of resources to do
> round(runif(nnoise,0,4095))
> but I couldn't think of a better way to get ints between 0 and 4095.
> (It's a waste because the random number generator makes unsigned long ints
> to begin with, then they are divided by 2^32 to get a double between 0
> and 1, and now I am undoing that!)

Compared to all the other inefficiencies going on, I don't think this
is worth worrying about (unless nnoise is *very* large). If you really
need this to be efficient, you could make a clone of runif in .C
callable code, and replace the floatingpoint (l / 2.^32) by a shift
operation (l >> 18 or thereabouts).

> I guess there is sample(,replace=true), which seems even worse for
> wasted resources. Maybe not.

Most likely it is...

-- 
   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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