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

François Pinard pinard at iro.umontreal.ca
Sun Jul 16 03:34:40 CEST 2006

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


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))

S is designed to allow you to work with "whole objects", which means that
for loops can (and should) be avoided.


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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----- End forwarded message -----

François Pinard   http://pinard.progiciels-bpi.ca

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