[R] (-1 as index) OR (envelope for QQ)
Peter Dalgaard BSA
p.dalgaard at biostat.ku.dk
Thu Feb 24 21:17:39 CET 2000
"Dan E. Kelley" <kelley at Phys.Ocean.Dal.CA> writes:
> Content-Type: TEXT/PLAIN; charset=US-ASCII
> I'm new to R (and to S) and am wondering about code from pages 72 and
> 83 of MASS (Venables+Ripley, 3rd edition), to draw an envelope on a QQ
> plot. Copying from the book, I've got:
> #... code whose gist is "a.fit <- nls(..."
> num.points <- length(resid(a.fit))
> qqnorm(residuals(a.fit)) # illustrate data-model residuals
> samp <- cbind(residuals(a.fit), matrix(rnorm(num.points*19),num.points,19))
> samp <- apply(scale(samp), 2, sort)
> rs <- samp[,1]
> xs <- qqnorm(rs, plot=FALSE)$x
> env <- t(apply(samp[,-1], 1, range)) ###########################3
> xyul <- par("usr")
> smidge <- min(diff(c(xyul, xs, xyul)))/2
> segments(xs-smidge,env[,1], xs+smidge, env[,1])
> segments(xs-smidge,env[,2], xs+smidge, env[,2])
> 1) You idiot! QQ plots are supposed to have standardized residuals of
> the data-model misfit. Do that and the QQ envelop is ok.
> 2) Don't copy S stuff into R code. The S code "samp[,-1]" from VR
> should be written "..." for use in R.
> 3) Don't be so rude as to ask such questions (with length attachments,
> no less) on a group like this. Give us a break!
> ... but I'm hoping that the mode won't be in the final category!
Well, 2) is *not* the answer... Try removing the plot=F from the 2nd
qqnorm and I think you'll see the light. Notice the scale on the y
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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