What about: my.df<-data.frame(x=rnorm(20),y=rep(0,20),z=rep(1,20)) my.df[,!apply(my.df,2,sd)==0,drop=F] This uses the fact that a column with eaqual values has a standard deviation of 0. Regards Wayne -----Original Message----- From: Jinsong Zhao [mailto:jinsong_zh@yahoo.com] Sent: 03 August 2004 09:43 To: R-Help Subject: [R] How to select a whole column? Thanks! Dear all, I hope to remove a whole column from a data frame or matrix (> 2000 columns). All value in the column are same. The first thing is to select those columns. For instance, I hope to remove the V3~6 column, for all the value in those colume is zero. V3 V4 V5 V6 V7 V8 V9 V10 1 0 0 0 0 0.000 0.000 0.000 0.000 2 0 0 0 0 0.000 0.000 0.000 0.000 3 0 0 0 0 0.000 0.000 0.000 0.000 4 0 0 0 0 0.000 0.000 0.000 0.000 5 0 0 0 0 0.000 0.000 0.000 0.000 6 0 0 0 0 -0.001 -0.001 -0.001 -0.001 7 0 0 0 0 0.000 0.000 0.000 -0.001 8 0 0 0 0 0.000 0.000 0.000 -0.001 9 0 0 0 0 -0.009 -0.012 -0.015 -0.018 I mean how to select the first four columns. Thank you very much for your consideration on this matter. Best wishes, Jinsong ===== (Mr.) Jinsong Zhao Ph.D. Candidate School of the Environment Nanjing University 22 Hankou Road, Nanjing 210093 P.R. China E-mail: jinsong_zh@yahoo.com ______________________________________________ R-help@stat.math.ethz.ch mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html KSS Ltd Seventh Floor St James's Buildings 79 Oxford Street Manchester M1 6SS England Company Registration Number 2800886 Tel: +44 (0) 161 228 0040 Fax: +44 (0) 161 236 6305 mailto:kssg@kssg.com http://www.kssg.com The information in this Internet email is confidential and m...{{dropped}}