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

[John Maindonald]

Dear John -
The title above the graph is also redundant for the first of the  
plots; do we want to be totally consistent?  I am not sure.

It occurs to me that the text "Cook's distance", as well as the  
contours, might be in red.
Regards
John.

John Maindonald             email: john.maindon...@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.


On 18/02/2009, at 12:27 PM, John Fox wrote:

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-boun...@r-project.org [mailto:r-devel-boun...@r-project.org 
]
On
Behalf Of John Maindonald
Sent: February-17-09 5:54 PM
To: r-devel@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.maindon...@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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