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}}


