[R] Subsetting a dataframe by dynamic column name

[David Carlson]

That only requires two small changes in Sarah's first solution:

> Finaldata[, !colnames(Finaldata) %in% V$v2[V$v1 == 1]]
      Length       Rate
1 0.53607323 0.01739951
2 0.15405615 0.11837908
3 0.04542388 0.53702702
4 0.15633703 0.68870041
5 0.35293973 0.38258981

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352


-----Original Message-----
From: r-help-bounces at r-project.org
[mailto:r-help-bounces at r-project.org] On Behalf Of Sneha Bishnoi
Sent: Thursday, March 27, 2014 11:06 AM
To: Sarah Goslee
Cc: r-help
Subject: Re: [R] Subsetting a dataframe by dynamic column name

Hi Sarah,

Thanks! Do agree its over complicated.
However looking at the solutions I think I did not state my
problem
completely.
V provides choices for only certain set of columns in Finaldata.
So v2 may not represent all columns of Finaldata.
I want to retain columns not provided as a choice for users plus
the ones
user chooses to keep.

Thanks!



On Thu, Mar 27, 2014 at 11:30 AM, Sarah Goslee
<sarah.goslee at gmail.com>wrote:

> There are many ways. You're making it overly complicated
>
> Here, in an actual reproducible example (as you were requested
to submit):
>
> V <- data.frame(v1=c(1,0,0), v2=c("Shape", "Length", "Rate"),
> stringsAsFactors=FALSE)
> Finaldata <- data.frame(Shape = runif(5), Length = runif(5),
Rate =
> runif(5))
>
> # assuming names in V are not in the same order as columns in
Finaldata
> # also assuming there might accidentally be names not in
Finaldata
> Finaldata[, colnames(Finaldata) %in% V$v2[V$v1 == 0]]
>
> # more elegant?
> Finaldata[, colnames(Finaldata) %in% V$v2[!V$v1]]
>
> # not robust to errors in V
> Finaldata[, V$v2[!V$v1]]
>
> # assumes order of column names matches order of V
> Finaldata[, -V$v1]
>
> Sarah
>
> On Thu, Mar 27, 2014 at 11:09 AM, Sneha Bishnoi
<sneha.bishnoi at gmail.com>
> wrote:
> > Hi all!
> >
> > I am trying to drop columns from a data frame dynamically
depending on
> user
> > input. The dataframe whose columns need to be dropped is
called
> "Finaldata"
> > So here is what I do:
> >
> > V is a dataframe with columns v1 and v2 as follows
> >
> >    v1          v2
> > 1   1      Shape
> > 2   0       Length
> > 3   0       Rate
> >
> > v1 corresponds to user input, 1 if you want to drop the
column, 0
> otherwise
> > v2 corresponds to column names of the all the columns in
"Finaldata"
> > I then use following code to drop columns
> >
> > for (i in 1:3)
> >   {
> >     if(V$v1[i]==1)
> >     {
> >       print(V$v2[i])
> >       Finaldata<-subset(Finaldata,select=-c(V$v2[i]))
> >     }
> >
> >   }
> >
> > However v2 being type character is not accepted by subset.
> > I read subset needs column names without quotes.
> > I tried stripping off quotes through gsub and cat,however it
din't help
> > There are lot of columns and I cannot perform this
individually on all
> > columns.
> > How do i go about it?
> >
> >
> > Thanks!
> > SB
> >
>
> --
> Sarah Goslee
> http://www.functionaldiversity.org
>



-- 
Sneha Bishnoi
+14047235469
H. Milton Stewart School of Industrial &  Systems Engineering
Georgia Tech

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