[R] What is the best method to produce means by categorical factors?

[ONKELINX, Thierry]

Dear Pat,

Have a look at recast from the reshape package.

library(reshape)
dataset <- expand.grid(factor1 = c("A", "B"), factor2 = c("C", "D"), Rep
= 1:3)
dataset$variable1 <- rnorm(nrow(dataset))
dataset$variable2 <- rnorm(nrow(dataset), mean = 10)
recast(factor1 + factor2 + variable ~ ., data = dataset, id.var =
c("factor1", "factor2", "Rep"), fun = mean) 

HTH,

Thierry

------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-----Oorspronkelijk bericht-----
Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
Namens Pat Schmitz
Verzonden: donderdag 30 juli 2009 10:19
Aan: r-help at r-project.org
Onderwerp: [R] What is the best method to produce means by categorical
factors?

I am attempting to replicate some of my experience from SAS in R and
assume there are best methods for using a combination of summary(),
subset, and
which() to produce a subset of mean values by categorical or ordinal
factors.

within sas I would write

proc means mean data=dataset;
class factor1 factor2
var variable1 variable2;
RUN;

producing an output with means for each variable by factor groupings as
below:

*factor1        factor2          obs       variable    mean*
Level A        treatmentA        3        variable1    10
                                          variable2    22

               treatmentB        3        variable1    12
                                          variable2    30

Level B        treatmentA        3        variable1    10
                                          variable2    22

               treatmentB        3        variable1    12
                                          variable2    30

What is the best way to go about this in R?






--
Patrick Schmitz
Graduate Student
Plant Biology
1206 West Gregory Drive
RM 1500

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