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

From: John Fox <jfox_at_mcmaster.ca>
Date: Tue, 17 Feb 2009 20:27:21 -0500

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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