[Rd] plot.lm: "Cook's distance" label can overplot point labels

[John Fox]

Dear John,

It occurs to me that the title above the graph, "Residuals vs. Leverage," is
entirely redundant since the x-axis is labelled "Leverage" and the y-axis
"Studentized residuals." Why not use the title above the graph for "Cook's
distance countours"?

Regards,
 John

> -----Original Message-----
> From: r-devel-bounces at r-project.org [mailto:r-devel-bounces at r-project.org]
On
> Behalf Of John Maindonald
> Sent: February-17-09 5:54 PM
> To: r-devel at r-project.org
> Cc: Martin Maechler
> Subject: [Rd] plot.lm: "Cook's distance" label can overplot point labels
> 
> The following code demonstrates an annoyance with plot.lm():
> 
> library(DAAGxtras)
> x11(width=3.75, height=4)
> nihills.lm <- lm(log(time) ~ log(dist) + log(climb), data = nihills)
> plot(nihills.lm, which=5)
> 
> OR try the following
> xy <- data.frame(x=c(3,1:5), y=c(-2, 1:5))
> plot(lm(y ~ x, data=xy), which=5)
> 
> The "Cook's distance" text overplots the label for the point with the
> smallest residual.  This is an issue when the size of the plot is much
> less than the default, and the pointsize is not reduced proportionately.
> 
> 
> I suggest the following:
>        xx <- hii
>        xx[xx >= 1] <- NA
> ## Insert new code
>        fracht <- (1.25*par()$cin[2])/par()$pin[2]
>        ylim[1] <- ylim[1] - diff(ylim)*max(0, fracht-0.04)
> ## End insert new code
>        plot(xx, rsp, xlim = c(0, max(xx, na.rm = TRUE)),
>             ylim = ylim, main = main, xlab = "Leverage",
>             ylab = ylab5, type = "n", ...)
> 
> Then, about 15 lines further down, replace
>          legend("bottomleft", legend = "Cook's distance",
>                 lty = 2, col = 2, bty = "n")
> 
> by
>          legend("bottomleft", legend = "Cook's distance",
>                 lty = 2, col = 2, bty = "n", y.intersp=0.5)
> 
> If this second change is not made, then one wants fracht <- (1.5*par()
> $cin[2])/par()$pin[2]
> I prefer the "Cook's distance" text to be a bit closer to the x-axis,
> as it separates it more clearly from any point labels.
> 
> John Maindonald             email: john.maindonald at anu.edu.au
> phone : +61 2 (6125)3473    fax  : +61 2(6125)5549
> Centre for Mathematics & Its Applications, Room 1194,
> John Dedman Mathematical Sciences Building (Building 27)
> Australian National University, Canberra ACT 0200.
> 
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