R help - Aug 2008 - Lattice: regression lines within grouped xyplot panels

Dear community,

I am looking for a possibility to draw 'regression lines' instead of 
'smooth' lines in grouped xyplots. The following code should give you a 
small example of the data structure.


library(lattice)
data(Gcsemv, package = "mlmRev")

# Creates artificial grouping variable ...
Gcsemv$Groups <-
   ifelse(as.numeric(as.character(Gcsemv$school))>65000,
          "Group1", "Group2")

xyplot(written ~ course | gender, data = Gcsemv,
        type = c("g", "p", "smooth"),
        groups = Groups,
        panel = function(x, y, ...) {
          panel.xyplot(x, y, ...)
# Here I want to draw the regression lines
#         panel.abline(x, y)
        },
        auto.key = list(space = 'right'))


I tried some variations like 'lm(y~x)' inside panel.abline() but had no 
success. Also googling around and reading in Deepayan Sakars interesting 
new book gave me no hints.

Is there any chance of displaying regression lines (instead of smooth 
function) within grouped panels? Or am I entirely wrong with this?

Thanks in advance,
Rainer Hurling



 > sessionInfo()
R version 2.7.1 Patched (2008-08-01 r46207)
i386-unknown-freebsd8.0

locale:
de_DE.ISO8859-15/de_DE.ISO8859-15/C/C/de_DE.ISO8859-15/de_DE.ISO8859-15

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] cclust_0.6-14   lattice_0.17-13 chron_2.3-24

loaded via a namespace (and not attached):
[1] grid_2.7.1  tools_2.7.1

On Fri, Aug 8, 2008 at 2:38 PM, Rainer Hurling <rhurlin at gwdg.de>
wrote:
> Dear community,
>
> I am looking for a possibility to draw 'regression lines' instead
of
> 'smooth' lines in grouped xyplots. The following code should give
you a
> small example of the data structure.
>
>
> library(lattice)
> data(Gcsemv, package = "mlmRev")
>
> # Creates artificial grouping variable ...
> Gcsemv$Groups <-
>  ifelse(as.numeric(as.character(Gcsemv$school))>65000,
>         "Group1", "Group2")
>
> xyplot(written ~ course | gender, data = Gcsemv,
>       type = c("g", "p", "smooth"),
>       groups = Groups,
>       panel = function(x, y, ...) {
>         panel.xyplot(x, y, ...)
> # Here I want to draw the regression lines
> #         panel.abline(x, y)
>       },
>       auto.key = list(space = 'right'))
Does this do what you want?:

xyplot(written ~ course | gender, data = Gcsemv,
      type = c("g", "p", "r"),
      groups = Groups)

The problem with your approach is that the panel function you define
doesn't deal with groups. An easy workaround is to use
panel.superpose:

xyplot(written ~ course | gender, data = Gcsemv,
      type = c("g", "p"),
      groups = Groups,
      panel = panel.superpose,
      panel.groups = function(x, y, ...) {
        panel.xyplot(x, y, ...)
        panel.lmline(x, y, ...)
      },
      auto.key = list(space = 'right'))

-Deepayan