R help - Jan 2012 - question: how to select a column from a dataframe in a function

Hi,

I am creating a function and ran into the problem of selecting a column
from a dataset. It seems as though the $ function (as in data$columnname)
does not apply in the function. In simplified version:

This works:
 testf2<-function(data,columnnumber){print(data[,columnnumber])}

But this doesn't:
testf<-function(data,column){print(data$column)}

Even though the first solution works, I would like to be able to insert the
columnname in the function, instead of the columnnumber. How do I do that?

Thank you in advance,

Julia

	[[alternative HTML version deleted]]

Just put the columnname variable into the brackets as well: they
accept strings.

As a general rule, always use the brackets (single or double) when
programming: `$` has some great features for interactive use but can
bite if you're not careful.

Michael

On Fri, Jan 13, 2012 at 5:34 PM, Julia Burggraaf <jmburggraaf at
gmail.com> wrote:
> Hi,
>
> I am creating a function and ran into the problem of selecting a column
> from a dataset. It seems as though the $ function (as in data$columnname)
> does not apply in the function. In simplified version:
>
> This works:
> ?testf2<-function(data,columnnumber){print(data[,columnnumber])}
>
> But this doesn't:
> testf<-function(data,column){print(data$column)}
>
> Even though the first solution works, I would like to be able to insert the
> columnname in the function, instead of the columnnumber. How do I do that?
>
> Thank you in advance,
>
> Julia
>
> ? ? ? ?[[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.

Hi
> 
> Hi,
> 
> I am creating a function and ran into the problem of selecting a column
> from a dataset. It seems as though the $ function (as in 
data$columnname)
> does not apply in the function. In simplified version:
> 
> This works:
>  testf2<-function(data,columnnumber){print(data[,columnnumber])}
> 
> But this doesn't:
> testf<-function(data,column){print(data$column)}
> 
> Even though the first solution works, I would like to be able to insert 
the
> columnname in the function, instead of the columnnumber. How do I do 
that?

Not sure if you get any answer yet.

testf2<-function(data,columnname){print(data[,columnname])}

Petr
> 
> Thank you in advance,
> 
> Julia
> 
>    [[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.