[R] Running an ANOVA with a BY

Tobias Verbeke tobias.verbeke at gmail.com
Mon Sep 28 18:58:24 CEST 2009

baxterj wrote:
> I have a simple 1 way anova coded like
> summary(ANOVA1way <- aov(Value ~ WellID, data = welldata))
> How can I use the BY function to do this ANOVA for each group using another
> variable in the dataset??  I tried coding it like this, but it doesn't seem
> to work.
> summary(ANOVA1way <- by(welldata, Analyte, function(x) aov(Value ~ WellID,
> data = welldata)))
> In SAS I would code it like this:
> Proc sort data=welldata; by analyte; run;
> Proc glm data=welldata;
> by analyte;
> class wellid;
> model value = wellid;
> run;

Look at the plyr package for a general solution to
this type of problems:


and its introductory guide on the package home page:



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