R help - Feb 2009 - 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

	[[alternative HTML version deleted]]

One way is to use %in% like below:

df<-data.frame(var.a=rnorm(10), var.b=rnorm(10),var.c=rnorm(10))
print(df)
df <- df[,!(names(df) %in% c('var.a','var.b')),drop=FALSE]
print(df)



On Tue, Feb 24, 2009 at  3:10 PM, Sean Zhang wrote:
> 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
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Setting to NULL works only if a single column is selected.
More generally,

df[, !(colnames(df) %in% c("var.b", "var.c")), drop=FALSE]

-Christos  
> -----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
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
>

Another way is:
> subset(df, select=c(var.b, var.c))
though I'd be willing to bet that using %in% is probably faster.[1]

Tony

[1] Unfortuantly I'm skint :-(

On 24 Feb, 20:10, Sean Zhang <seane... at gmail.com>
wrote:
> 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
>
> ? ? ? ? [[alternative HTML version deleted]]
>
> ______________________________________________
> R-h... at r-project.org mailing
listhttps://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guidehttp://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.