R help - Jan 2004 - Trellis graph and two colors display

Hello,

I would like to display two groups of dots in different colors or style and
additionnaly a linear regression for all the dots in
panel plots of a Trellis graph.  Actually to get in each panel the equivalent
of:

plot(x[mois==3],y[mois==3],col="blue")
points(x[mois==9],y[mois==9],col="red")
abline(lm(y~x), col="green")

"mois" being a grouping variable and ID (see below) the conditioning
variable in a data.frame of 230 rows

After several really disatreous trials, I have tried the following:

xyplot(y~x|ID,panel=function(x,y){panel.superpose(x,y,subscripts=1:230,groups=mois);panel.abline(lm(y~x),col="green")})

1/ I am not sure to have well understood what  the role of subscripts (with no
default) is in the function panel.superpose and if
the values passed are appropriate here;

2/ this apparently displays all the points without changes of style between
groups (neither symbols or colors).

3/ this does not allow changes in color for points display

Can anybody give me a hint on where I am wrong?

Sorry to be probably very clumpsy,

Kind regards,

Patrick Giraudoux

>From: "Patrick Giraudoux" <patrick.giraudoux at
univ-fcomte.fr>
>
>Hello,
>
>I would like to display two groups of dots in different colors 
>or style and additionnaly a linear regression for all the dots in
>panel plots of a Trellis graph.  Actually to get in each panel 
>the equivalent of:
>
>plot(x[mois==3],y[mois==3],col="blue")
>points(x[mois==9],y[mois==9],col="red")
>abline(lm(y~x), col="green")
>
>"mois" being a grouping variable and ID (see below) the 
>conditioning variable in a data.frame of 230 rows
>
>After several really disatreous trials, I have tried the following:
>
>xyplot(y~x|ID,panel=function(x,y){panel.superpose(x,y,subscript
>s=1:230,groups=mois);panel.abline(lm(y~x),col="green")})
>
You don't need to mess around with the subscripts argument for this. I think
the problem is that you are not passing the necessary graphical parameters
to your panel function. You could do:

dat <- expand.grid(ID = 1:4, mois = c(3, 9))
dat <- dat[rep(seq(nrow(dat)), rep(10, nrow(dat))), ]
dat <- data.frame(dat, x = rnorm(nrow(dat)), y = rnorm(nrow(dat)))
dat$ID <- factor(dat$ID)

lset(list(superpose.symbol = list(col = c("blue", "red"),
pch = c(1, 1))))

xyplot(y ~ x | ID, data = dat,
       groups = mois,
       panel = function(x, y, ...) {
         panel.superpose(x, y, ...)
         panel.abline(lm(y~x), col = "green")
       })

Cheers,
Jim 

James A. Rogers 
Manager, Biometrics
PGR&D Groton Labs
Eastern Point Road (MS 8260-1331)
Groton, CT 06340
office: (860) 686-0786
fax: (860) 715-5445
 


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