[R] Deleting many columns of a data frame with the same name ina row

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Steve Lianoglou
> Sent: Tuesday, February 02, 2010 9:05 AM
> To: anna
> Cc: r-help at r-project.org
> Subject: Re: [R] Deleting many columns of a data frame with 
> the same name ina row
> 
> Hi,
> 
> On Tue, Feb 2, 2010 at 11:47 AM, anna 
> <lippelanna24 at hotmail.com> wrote:
> >
> > This is what I just found now but I guess there is a simpler way:
> >
> > 
> datas[which(names(datas)=="A")]<-list(rep(NULL,length(which(na
mes(datas)=="A"))))
> > but it worked
> 
> For what it's worth, you could also have done:
> 
> clean <- datas[,-which(names(datas)=="A")]
> 
> (note that indexing with a "negative" vector removes those
> rows/columns from your object (instead of picking them)).

I would recommend replacing
  datas[, -which(names(data)=="A")]
with   
  datas[, names(data)!="A"]
because the former returns a zero-column data.frame if there
are columns of datas named "A".  (which(rep(F,n))->integer(0)
and -integer(0) is identical to integer(0), which selects
no elements).  The latter returns the entire data.frame in
the case.

Logical subscripts are your friend.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com 

> 
> -steve
> 
> -- 
> Steve Lianoglou
> Graduate Student: Computational Systems Biology
>  | Memorial Sloan-Kettering Cancer Center
>  | Weill Medical College of Cornell University
> Contact Info: http://cbio.mskcc.org/~lianos/contact
> 
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