From: Afshartous, David <afshart_at_exchange.sba.miami.edu>

Date: Tue 12 Sep 2006 - 16:00:20 GMT

Date: Tue 12 Sep 2006 - 16:00:20 GMT

thanks to all for the quick replies!

dat <-data.frame(fact = as.factor(c(rep("A", 3),rep("B", 3), rep("C", 3))),Y = rnorm(9))
dat.new = dat[1:6, ]

dat.new$fact = dat$fact[1:6, drop = T]

-----Original Message-----

From: pd@pubhealth.ku.dk [mailto:pd@pubhealth.ku.dk] On Behalf Of Peter Dalgaard
Sent: Tuesday, September 12, 2006 11:45 AM
To: Afshartous, David

Cc: r-help@stat.math.ethz.ch

Subject: Re: [R] levels of factor when subsetting the factor

"Afshartous, David" <afshart@exchange.sba.miami.edu> writes:

*>
**> All,
**>
*

> When I take a subset of a factor the reduced factor still maintains

*> all the original levels of the factor when say forming the key in a plot.
**> The data is correct, but the variable still "remembers" the original
**> levels. See below for reproducible code. Does anyone know how to fix
**> this?
**> cheers,
**> dave
**>
**> fact = as.factor(c(rep("A", 3),rep("B", 3), rep("C", 3))) new.fact =
**> fact[1:6]
**> > new.fact
**> [1] A A A B B B
**> Levels: A B C ## should only show A B
*

Just use

> factor(new.fact)

[1] A A A B B B

Levels: A B

or

> fact[1:6, drop=T]

[1] A A A B B B

Levels: A B

And, no, it is not a bug. The fact that a subsample happens to consist only of males does not turn gender into a one-level factor... (Apart from the philosophy, it makes a real difference in tabulation.)

-- O__ ---- Peter Dalgaard ุster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.Received on Wed Sep 13 02:03:59 2006

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