[R-sig-ME] Unexpected text-output using BY to plot random effects.

[Dimitris Rizopoulos]

abline() does not return anything, it justs adds lines to the existing 
plot; this is why you obtain NULL from the by() statement. One option to 
avoid printing is to use invisible(), e.g.,

invisible(by(sleep, sleep$resp, function(x) abline(coef=x)))


I hope it helps.

Best,
Dimitris


Rense Nieuwenhuis wrote:
> Dear Helpers,
> 
> I have been trying to visualise the random effects of a mixed effects  
> model which was fitted with the lmer function from the lme4 package.  
> Extracting the fixed and random effects works rather well with  
> 'coef', but when plotting this with 'by' and 'abline', something  
> strange happens.
> 
> I use the following syntax (example):
> 
> fm1 <- lmer(Reaction ~ Days + (Days|Subject), sleepstudy)
> 
> sleep <- coef(fm1)$Subject
> sleep$resp <- 1:18
> 
> plot(c(0,10), c(200,400), type="n")
> 
> by(sleep, resp, function(x) abline(coef=x))
> 
> This results in a basic, but acceptable, plot. However, it also  
> results in quite some output at the R-Prompt. A portion of it looks  
> like this:
> 
> resp: 308
> NULL
> -----------------------------------------------------
> resp: 309
> NULL
> -----------------------------------------------------
> resp: 310
> NULL
> -----------------------------------------------------
> resp: 330
> NULL
> -----------------------------------------------------
> resp: 331
> NULL
> -----------------------------------------------------
> resp: 332
> NULL
> 
> 
> What is happening? I suspect it has something to do with my use of  
> the 'by' function, but is there a way to prevent all the unwanted  
> text-output?
> 
> Thanks in advance
> 
> Rense
> 
> 
> 
> 
> 
> - - -- --- ----- --------
> Rense Nieuwenhuis
> +31 6 481 05 683
> 
> www.rensenieuwenhuis.nl
> 
> 
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-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
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