look at ?"[.data.frame" and also check this:
dat <- data.frame(V1=c(1:12), F1=rep(letters[1:3], each=4)) dat.ac <- dat[dat$F1 !="b", ] ############### dat.ac$F1 dat.ac$F1[, drop=TRUE] ############### dat.ac$F1 <- dat.ac$F1[, drop=TRUE] levels(dat.ac$F1)
I hope it helps.
best, Dimitris
---- Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven
Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/16/336899 Fax: +32/16/337015 Web: http://www.med.kuleuven.ac.be/biostat/ http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm
----- Original Message ----- From: "Lefebure Tristan" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Monday, February 28, 2005 2:07 PM
Subject: [R] persistance of factor levels in a data frame
Hi, Just something I don't understand:
data <- data.frame(V1=c(1:12),F1=c(rep("a",4),rep("b",4),rep("c",4)))
data_ac <- data[which(data$F1 !="b"), ]
levels(data_ac$F1)
Why the level "b" is always present ?
thanks
Tristan, R 2.0.1 for Linux Fedora 3
-- ------------------------------------------------------------ Tristan LEFEBURE Laboratoire d'�cologie des hydrosyst�mes fluviaux (UMR 5023) Universit� Lyon I - Campus de la Doua Bat. Darwin C 69622 Villeurbanne - France
Phone: (33) (0)4 26 23 44 02 Fax: (33) (0)4 72 43 15 23
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