R help - May 2009 - How to exclude a column by name?

Given an arbitrary data frame, it is easy to exclude a column given its index:
df[,-2].  How to do the same thing given the column name?  A naive attempt
df[,-"name"] did not work :)

Zeljko Vrba wrote:
> Given an arbitrary data frame, it is easy to exclude a column given its
index:
> df[,-2].  How to do the same thing given the column name?  A naive attempt
> df[,-"name"] did not work :)
>
> ______________________________________________
> 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,

This piece of code does the trick. Most important is the which() command:

df = data.frame(a = runif(10), b = runif(10))
df[,-which(names(df) == "a")]

cheers,
Paul

-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone:  +3130 274 3113 Mon-Tue
Phone:  +3130 253 5773 Wed-Fri
http://intamap.geo.uu.nl/~paul

Hope this helps:
> df <- data.frame(matrix(1:10,2))
> df
  X1 X2 X3 X4 X5
1  1  3  5  7  9
2  2  4  6  8 10
> df[,-2]
  X1 X3 X4 X5
1  1  5  7  9
2  2  6  8 10
> df[,-which(names(df)=="X2")]
  X1 X3 X4 X5
1  1  5  7  9
2  2  6  8 10


On Wed, May 27, 2009 at 6:37 PM, Zeljko Vrba <zvrba at ifi.uio.no>
wrote:
> Given an arbitrary data frame, it is easy to exclude a column given its
index:
> df[,-2]. ?How to do the same thing given the column name? ?A naive attempt
> df[,-"name"] did not work :)

On Wed, May 27, 2009 at 12:52:41PM +0200, Paul Hiemstra
wrote:
> 
> This piece of code does the trick. Most important is the which() command:
> 
> df = data.frame(a = runif(10), b = runif(10))
> df[,-which(names(df) == "a")]
> 
Thanks to you and Linlin.  It did not occur to me to use which(); I thought
that there would be a shorter way to accomplish this since names are
first-class indices for data frames and arrays.  (Or are they?  What happens
under the hood when I write df[,"a"]?)

You can try this:

DF[,"columnName"] <- NULL

On Wed, May 27, 2009 at 7:37 AM, Zeljko Vrba <zvrba@ifi.uio.no> wrote:
> Given an arbitrary data frame, it is easy to exclude a column given its
> index:
> df[,-2].  How to do the same thing given the column name?  A naive attempt
> df[,-"name"] did not work :)
>
> ______________________________________________
> 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.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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On Wed, May 27, 2009 at 6:37 AM, Zeljko Vrba <zvrba@ifi.uio.no> wrote:
> Given an arbitrary data frame, it is easy to exclude a column given its
> index:
> df[,-2].  How to do the same thing given the column name?  A naive attempt
> df[,-"name"] did not work :)
>
Various ways:

Boolean index vector:

    df[ , names(df) != "name" ]

List of wanted column names:

    df[ , setdiff(names(df), "name") ]

Negated list of unwanted column indexes:

   df[ , -match("name",names(df)) ]
   df[ , -which(names(df) == "name") ]

The special 'subset' hack for column names; beware, I think this is the
only
place in R where you can negate a column name.

   subset(df , select = -a )

Hope this helps,

         -s

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