R-beta: quantile

[Martin Maechler]

	[diverted from R-help to R-devel]

>>>>> "PD" == Peter Dalgaard BSA <p.dalgaard@biostat.ku.dk> writes:

    PD> Bill Simpson <wsimpson@uwinnipeg.ca> writes:
    >> 
    >> I do:
    >> x<-rnorm(1000)
    >> quantile(x,c(.025,.975))
    >> 2%       98% 
    >> -1.844753  1.931762 
    >> 
Yes, this is a pain;
I've known about this for months, and always been too busy / diverted 
to fix it..

    >> Since I want to find a 95% confidence interval, I take the .025 and .975
    >> quantiles.  HOWEVER R says I have the 2% (not 2.5%) and 98% (not 97.5%)
    >> points.  Is it just rounding the printed 2% and 98%, or is it REALLY
    >> finding .02 and .98 points instead of .025 and .975?

    PD> It's rounding... 

    PD> At the end of the quantile function, you'll see:

    PD> names(qs) <- paste(round(100 * probs), "%", sep = "")
    PD> qs
    PD> }

    PD> Maybe we should put in an extra argument for controlling the precision
    PD> of the rounding?

Hmm, I think we agree that we should improve that 'names(gs)..' line.

However, the first step should be to use a much better default than
	round(100 * probs)
If the default is ``smart enough'', 
maybe we don't really need a new argument
[Can still have one for the ones who really want to fine-tune the names..]

-------------

Some untested proposals for replacement of   
	round(100 * probs)	


1)  formatC(100*probs, dig=3,				 format='f')
2)  formatC(100*probs, dig= max(3, .Options$digits - 3), format='f')
3)  signif(100*probs,       max(3, .Options$digits - 3))

or then replace  "max(3, .Options$digits - 3)"
by the new argument  'digits.names'
and have that one default to
	digits.names = max(3, .Options$digits - 3)


Martin
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