[R] How to select a whole column? Thanks!

Wayne Jones
2004-08-03T08:50:05Z

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

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