Filter out some levels?

how is it possible t cut some levels from one factor to  subsetting  a 
data.frame on?

subdata <- subset(data, data$FACTOR="1" | 
data$FACTOR="BETA" | data$FACTOR="XY")
???

Maybe a modifcation here is better, but how?
mergex[mergex$PLZX %in% levels(mergex$PLZX) ,]

Christian:

You need element by element comparison.  Does this help?

mydata <- data.frame(FACTOR = c("1", "BETA", "XY", "DROP"), Y = 
runif(4))

mydata[mydata$FACTOR=="1" | mydata$FACTOR=="XY" | 
mydata$FACTOR=="BETA",]

   FACTOR         Y
1      1 0.5111390
2   BETA 0.7219460
3     XY 0.1346707

mydata[mydata$FACTOR!="DROP",]

   FACTOR         Y
1      1 0.5111390
2   BETA 0.7219460
3     XY 0.1346707

See ?"=="

Chuck Cleland, Ph.D.
NDRI, Inc.
71 West 23rd Street, 8th floor
New York, NY 10010
tel: (212) 845-4495 (Tu, Th)
tel: (732) 452-1424 (M, W, F)
fax: (917) 438-0894