[Rd] Matrices given to pt? [was: [R] for loops and counters]

[Prof Brian Ripley]

There is a general rule that scalar operations (that is functions 
that work element-by-element and return a scalar result) preserve 
attributes including names, dims and dimnames.

Similarly, there is a general rule about binary operations and attributes.

These things should definitely be in the `R Language Definition', but that 
languishes as a draft.  I am writing up comments on R internals (currently 
an appendix on `Writing R Extensions', and this will go there (the section 
on attributes is current work).

On Sat, 15 Jul 2006, François Pinard wrote:

> Hi, people.
> 
> I was a bit intrigued by the message quoted below.  Indeed, if pt() is 
> given a matrix, it returns a matrix.  Should this feature be documented?
> ?pt speaks about "a vector of quantiles", and says nothing about the 
> type of what it returns.
> 
> The same might presumably apply to other distribution-related functions.
> 
> ----- Forwarded message from Martyn Plummer <plummer at iarc.fr> -----
> 
> From: Martyn Plummer <plummer at iarc.fr>
> Date: Thu Apr 10 10:07:01 2003
> Subject: [R] for loops and counters
> 
> Peter, 
> 
> You didn't say what goes wrong, but you mind find this version more useful
> 
> tstat <- (matrix(means, k,k, byrow=TRUE) - matrix(means, k,k,byrow=FALSE))/rms
> pvalue <- 2*(1-pt(abs(tstat), df=df))
> pvalue[upper.tri(pvalue)]
> 
> S is designed to allow you to work with "whole objects", which means that
> for loops can (and should) be avoided.
> 
> Martyn
> 
> On 05-Oct-99 Peter B. Mandeville wrote:
> > I am trying to assign values to a vector (pvalue). Similar code works in C
> > but not in R. What am I doing wrong?
> 
> >       r <- pvalue <- 0
> >       for(i in (1:(k-1))){
> >               for(j in (i+1):k){
> >                       r <- r+1
> >                       tstat <- (means[i]-means[j])/rms
> >                       pvalue[r] <- 2*(1-pt(abs(tstat),df))
> >               }
> >       }
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595