subset problem (reducing from six to two levels)

Ine wrote:

Hi all,
I have got a seemingly simple problem (I am an R starter) with subsetting
my
data set, but cannot figure out the solution: I want to subset a data set
from six to two levels, so that all analyses are done only with these two
remaining levels.
I tried

TOTAL<-read.delim('total.csv',header=T)
SUBSET.OF.TOTAL<-subset(TOTAL, FactorX %in% c("Level1","Level2"))
attach(SUBSET.OF.TOTAL)

but R does not eliminate the remaining levels of FactorX, just assigns
'not
available' to the data. Like this, the other levels still show up in
plots
etc., but without data entries. Anybody got a solution how to subset the
data so that I eliminate the other levels completely?

Thanks a lot for the help,

R does not "assign 'not available'" (look at the subsetted data).

However, factors do not lose levels just because they are not present in 
a subset of data. There are good reasons for that, but let's not go 
there this time (look in the list archives if you care). To get rid of 
unwanted levels, use

FactorXX <- factor(FactorX, levels=c("Level1","Level2"))

or just factor(FactorX) if you know that both levels are present (or 
don't care).


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