[R] rlm results on trellis plot

[Bert Gunter]

I don't think the code below does what's requested, as it assumes a single
overall fit for all panels, and I think the requester wanted separate fits
by panel. This can be easily done, of course, by a minor modification:

xyplot( y ~ x | z,
     panel = function(x,y,...){
	   panel.xyplot(x,y,...)
	   panel.abline(lm(y~x),col="blue",lwd=2)
	   panel.abline(rlm(y~x),col = "red",lwd=2)
	})

Note that the coefficients do not need to be explicitly extracted by coef(),
as panel.abline will do this automatically.

Bert Gunter
Genentech Nonclinical Statistics
South San Francisco, CA 94404
650-467-7374



Alan S Barnett wrote:
> How do I add to a trellis plot the best fit line from a robust fit? I
> can use panel.lm to add a least squares fit, but there is no panel.rlm
> function.

  How about using panel.abline() instead of panel.lmline()?

fit1 <- coef(lm(stack.loss ~ Air.Flow, data = stackloss))
fit2 <- coef(rlm(stack.loss ~ Air.Flow, data = stackloss))

xyplot(stack.loss ~ Air.Flow, data=stackloss,
       panel = function(x, y, ...){
         panel.xyplot(x, y, ...)
         panel.abline(fit1, type="l", col="blue")
         panel.abline(fit2, type="l", col="red")
       }, aspect=1)

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