[R] add trend line to each group of data in: xyplot(y1+y2 ~ x | grp...

[Andy Bunn]

> -----Original Message-----
> From: Deepayan Sarkar [mailto:deepayan.sarkar at gmail.com]
> Sent: Friday, March 10, 2006 4:10 PM
> To: Andy Bunn
> Cc: R-Help
> Subject: Re: add trend line to each group of data in: xyplot(y1+y2 ~ x |
> grp...
> 
> 
> On 3/10/06, Andy Bunn <abunn at whrc.org> wrote:
> > Although this should be trivial, I'm having a spot of trouble.
> >
> > I want to make a lattice plot of the format y1+y2 ~ x | grp but 
> then fit a
> > lm to each y variable and add an abline of those models in 
> different colors.
> > If the xyplot followed y~x|grp I would write a panel function 
> as below, but
> > I'm unsure of how to do that with y1 and y2 without reshaping the data
> > before hand. Thoughts appreciated. -Andy
> >
> >
> >
> > foo <- data.frame(y1 = 1:25+rnorm(100, -3, 1), y2 = 
> 1:25+rnorm(100,3,1), x =
> > rep(1:25,4), grp = rep(letters[1:4],25))
> > # I want to add a trend line for y1 and y2 here:
> > xyplot(y1+y2 ~ x | grp, data = foo)
> > # like this example for just one y variable:
> > xyplot(y1~x|grp, data = foo, panel = function(x,y)
> >           { lm1 = lm(y~x)
> >             panel.points(x,y, col = "red")
> >             panel.abline(lm1, col = "red")
> >             #lm2 = lm(y~x) # model for y2
> >             #panel.points(x,y, col = "blue") #points for y2
> >             #panel.abline(lm2, col = "blue") #abline for y2
> >           })
> 
> Depending on at what level your question approximates your real question,
> 
> xyplot(y1+y2~x|grp, data = foo, type = c('r', 'p'))
> 
> or
> 
> xyplot(y1+y2~x|grp, data = foo, panel = panel.superpose,
>            panel.groups = function(x,y,...)
>           { lm1 = lm(y~x)
>             panel.points(x,y, col = "red")
>             panel.abline(lm1, col = "red")
>             #lm2 = lm(y~x) # model for y2
>             #panel.points(x,y, col = "blue") #points for y2
>             #panel.abline(lm2, col = "blue") #abline for y2
>           })
> 
> (the body of the function is unchanged, but the argument list has a
> ..., which is important).
> 
> Deepayan
> --
> http://www.stat.wisc.edu/~deepayan/

Deepayan:

I'm really trying to understand how to access the different groups in this type of plot. Imagine I have the same scenario as above, an xyplot of the form y1+y2 ~ x | grp. Now, how can I modify the call to panel.text to write, say, the correlation coeff from each model to different portions of each panel (the upper left corner for the correlation of (x,y2) and the lower right corner for x,y2). The code below, if uncommented, executes but obviously doesn't do what I want it to do. Thoughts appreciated and gratitude as always. -Andy


foo <- data.frame(y1 = 1:25+rnorm(100, -3, 1), y2 = 1:25+rnorm(100,3,1), x = rep(1:25,4), grp = rep(letters[1:4],25))
y.range <- range(foo$y1, foo$y2)
x.range <- range(foo$x)
xyplot(y1+y2~x|grp, data = foo, panel = panel.superpose, 
       col.line=c('red','blue'), col.symbol=c('red','blue'), panel.groups = function(x,y,col.line,col.symbol,...)
          { panel.points(x,y,col=col.symbol)
            panel.lmline(x,y,col=col.line)
#            # if the data being plotted are from y1 then
#            # write the cor coef in the lower right corner
#            aCor=round(cor(x,y),digits=2)
#            panel.text(x.range[2],y.range[1],paste("r=,",aCor),pos=2,col="red")
#            # if the data being plotted are from y2 then
#            # write the cor coef in the upper left corner
#            aCor=round(cor(x,y),digits=2)
#            panel.text(x.range[1],y.range[2],paste("r=,",aCor),pos=4,col="blue")
          })