how to NULL multiple variables of a df efficiently?

-----Original Message-----
From: r-help-bounces at r-project.org 
[mailto:r-help-bounces at r-project.org] On Behalf Of Sean Zhang
Sent: Tuesday, February 24, 2009 3:10 PM
To: r-help at r-project.org
Subject: [R] how to NULL multiple variables of a df efficiently?

Dear R-helpers:

I am an R novice and would appreciate answer to the following 
question.

Want to delete many variables in a dataframe.
Am able to delete one variable by assigning it as NULL Have a 
large number of variables and would like to delete them 
without using a for loop.

Is there a command/function which does this job?

Many thanks in advance.

-Sean


#Small Example:

df<-data.frame(var.a=rnorm(10), var.b=rnorm(10),var.c=rnorm(10))
df[,'var.a']<-NULL   #this works for one single variable
df[,c('var.a','var.b')]<-NULL  #does not work for multiple variables

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