
In absence of workable code, I assume you are trying to find the mean of column by referring to its name (which is read from another file). 
try...v<-mean(Dataset[, paste(varlist[i])])
Kulwinder 

> From: dwinsemius@comcast.net
> To: jween@klaru-baycrest.on.ca
> Date: Wed, 24 Feb 2010 20:56:26 -0500
> CC: r-help@r-project.org
> Subject: Re: [R] variable substitution in for loops
> 
> 
> On Feb 24, 2010, at 8:18 PM, Jon Erik Ween wrote:
> 
> > Friends
> >
> > I can't quite find a direct answer to this question from the lists,  
> > so here goes:
> >
> > I have several dataframes, 200+ columns 2000+ rows. I wish to script  
> > some operations to perform on some of the variables (columns) in the  
> > data frames not knowing what the column number is, hence have to  
> > refer by name. I have variable names in a text file "varlist". So,  
> > something like this:
> >
> > for (i in 1:length(varlist)){
> > 	j<-varlist[i]
> > 	v<-mean(Dataset[[j]])
> > 	print(v)
> > }
> 
> Without a data example this is untested guesswork and may fail if  
> varlist is not a vector or something that can be coerced to a vector.  
> Might help to look at str(varlist),  ...  anyway ...
> 
> 
> for (i in varlist){
> 	
> 	v<-mean(Dataset[ , i])
> 	print(v)
> }
> 
> 
> If it doesn't work, then pay close attention to the error messages.
> -- 
> David
> 
> 
> >
> > Now, if I force it
> >
> > j<-"Var1"
> > v<-mean(Dataset[[j]])
> > print(v)
> >
> > then it works, but not if i read the varlist as above.
> >
> > Looking at "j" I get:
> >
> >> print(j)
> >          V1
> > 1 Var1
> 
> Right. You are supplying a list as an index.
> 
> >
> > Hence there is a lot of other stuff read into "j" that confuses  
> > "mean".
> 
> I think it is confusing "[[", but it's really more guesswork because  
> you did not supply a reproducible example.
> 
> > I can't figure out how to just get the value of the variable and  
> > nothing else. I've tried space separated, comma separated, tab  
> > separated lists and all give the same error. I've tried get(),  
> > parse()... no go.
> >
> > Any suggestions?
> >
> > Thanks a lot
> >
> > Jon
> >
> > Soli Deo Gloria
> >
> > Jon Erik Ween, MD, MS
> > Scientist, Kunin-Lunenfeld Applied Research Unit
> > Director, Stroke Clinic, Brain Health Clinic, Baycrest Centre
> > Assistant Professor, Dept. of Medicine, Div. of Neurology
> >    University of Toronto Faculty of Medicine
> >
> > Kimel Family Building, 6th Floor, Room 644
> > Baycrest Centre
> > 3560 Bathurst Street
> > Toronto, Ontario M6A 2E1
> > Canada
> >
> > Phone: 416-785-2500 x3648
> > Fax: 416-785-2484
> > Email: jween@klaru-baycrest.on.ca
> >
> >
> > Confidential: This communication and any attachment(s) may contain  
> > confidential or privileged information and is intended solely for  
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> >
> >
> > 	[[alternative HTML version deleted]]
> >
> > ______________________________________________
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> > 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.
> 
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
> 
> ______________________________________________
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