Unexpected text-output using BY to plot random effects.
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 [[alternative HTML version deleted]]
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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 Fax: +31/(0)10/7043014