Stavros Macrakis wrote:
> On Tue, Feb 24, 2009 at 3:10 PM, Sean Zhang wrote:
>
>> ...Want to delete many variables in a dataframe....
>> 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
>>
>
> Actually, setting to NULL works fine for multiple variables, but you
> need one NULL per variable:
>
>
>> df[,c("var.a","var.b")] <- list(NULL,NULL)
>>
actually, you need one NULL per variable, but it suffices to provide a
list of *one* NULL, and it will be recycled:
df[,c("var.a","var.b")] <- list(NULL)
>> df
>>
> var.c
> 1 1.2470314
> 2 -0.7075917
> 3 -1.3959612
>
> If the variable list is in a variable:
>
>
>> vars <- c("var.a","var.c")
>>
>
> Careful, rep requires a *list* of NULL, not an element:
>
>
>> df[,vars] <- rep(list(NULL),length(vars))
>>
as above, this works as well:
df[, vars] = list(NULL)
and this, simplest of them all, works too:
df[vars] = list(NULL)
vQ
______________________________________________
R-help@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.
