Based on your two first sentences I think the solution is to use
xyplot(y ~ x | facA, groups = facB, data = toydf,type=c("p","r"))
Try it and see if this is what you want.
Best regards
Frede Aakmann Tøgersen
Scientist
Danish Institute of Agricultural Sciences
Research Centre Foulum
Dept. of Genetics and Biotechnology
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> -----Oprindelig meddelelse-----
> Fra: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] På vegne af Sebastian Luque
> Sendt: 21. februar 2006 08:20
> Til: [email protected]
> Emne: [R] indexing within panels in xyplot
>
> Dear R-helpers,
>
> I need to show a linear fit through a subset of the data
> within each combination of levels of two factors. So I
> prepared an xyplot with different panels for each level of
> one of the factors, and different symbols within each panel
> for the levels of the second factor. My problem is selecting
> the subset of each combination through which the line should
> be fit for subsequent plotting. This hopefully shows the idea:
>
>
> ---<---------------cut here---------------start-------------->---
> toydf <- expand.grid(1:100, c("A", "B"),
> c("pop1", "pop2", "pop3", "pop4",
> "pop5")) toydf <- data.frame(facA = toydf[[3]], facB = toydf[[2]],
> x = toydf[[1]], y = rnorm(1000))
>
> xyplot(y ~ x | facA, groups = facB, data = toydf,
> panel.groups = function(x, y, subscripts, ...) {
> panel.xyplot(x, y, ...)
> lindx <- which(y[subscripts] == max(y[subscripts],
> na.rm = TRUE))
> xleft <- mean(x[lindx], na.rm = TRUE)
> fit <- lm(y[x >= xleft] ~ x[x >= xleft])
> panel.abline(fit)
> })
> ---<---------------cut here---------------end---------------->---
>
> i.e. the left limit for fitting the line is defined by the
> mean of x values where y is equal to the maximum y values,
> *within* each combination of levels of both factors. The
> above is giving me:
>
> Error in lm.fit(x, y, offset = offset, singular.ok =
> singular.ok, ...) :
> 0 (non-NA) cases
> In addition: Warning message:
> no finite arguments to max; returning -Inf
>
> which shows I'm not understanding how the 'subscripts' argument works.
> I'd appreciate some pointers on what I'm doing wrong, as I
> haven't been able to find help in the help pages and List archives.
>
> Thanks,
>
> --
> Sebastian P. Luque
>
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>
>
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