[R-sig-ME] plotting residuals vs. fitted values by group

[Rachel Cohen]

Hi, I am quite new to using R and am currently trying to plot the 
residuals vs. fitted values by group, taken from an lmer model within 
lme4_0.999375-36.  The model i'm using is:

mod5<-lmer((centre.log.mass)~centre.log.dbh+centre.log.height+(1+centre.log.height|species_site),REML=F) 


I have tried:
plot(mod5, resid(.)~fitted(.)|species_site)

but get the following error message:

Error in xy.coords(x, y, xlabel, ylabel, log) :
   'x' and 'y' lengths differ

I'm not sure what this means?  I have managed to plot the overall model 
residuals vs. fitted values by using:

fit<-fitted(mod5)
res<-resid(mod5)
plot(fit,res, main="Model V Residuals vs. Fitted Mass", ylab="Ln 
Residual", xlab="Ln Fitted Mass")

However, I'm not sure how to get an individual group-level plot for each 
of my 12 groups of residuals vs. fitted.

Any help would be greatly appreciated!

Rachel Cohen

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