R help - Apr 2003 - subsetting a dataframe

How does one remove a column from a data frame when the name of
the column to remove is stored in a variable?

For Example:

colname <- "LOT"

newdf <- subset(olddf,select = - colname)

The above statement will give an error, but thats what I'm trying to 
accomplish.

If I had used:

newdf <- subset(olddf,select = - LOT)

then it would have worked, but as I said the column name is stored in a 
variable
so I can't just enter it explicity.

Thanks.

> How does one remove a column from a data frame when the name of
> the column to remove is stored in a variable?
> 
> For Example:
> 
> colname <- "LOT"
> 
> newdf <- subset(olddf,select = - colname)

This is how I do it.  There are variations on this
and I'm sure totally different ways as well.

newdf <- newdf[, names(newdf) != colname]


If 'colnames' is a vector (i.e. if you have multiple columns
to delete) then do:


newdf <- newdf[, !(names(newdf) %in% colname)]

This command will work even if 'colname' is not a vector


Doug


 
> The above statement will give an error, but thats what I'm trying to 
> accomplish.
> 
> If I had used:
> 
> newdf <- subset(olddf,select = - LOT)
> 
> then it would have worked, but as I said the column name is stored in a 
> variable
> so I can't just enter it explicity.
> 
> Thanks.
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>

Dear Chris,

The following should work for you:

         olddf[[colname]] <- NULL

I hope this helps,
  John

At 11:28 AM 4/7/2003 -0700, Chris Handorf wrote:
>How does one remove a column from a data frame when the name of
>the column to remove is stored in a variable?
>
>For Example:
>
>colname <- "LOT"
>
>newdf <- subset(olddf,select = - colname)
>
>The above statement will give an error, but thats what I'm trying to 
>accomplish.
>
>If I had used:
>
>newdf <- subset(olddf,select = - LOT)
>
>then it would have worked, but as I said the column name is stored in a 
>variable
>so I can't just enter it explicity.
____________________________
John Fox
Department of Sociology
McMaster University
email: jfox at mcmaster.ca
web: http://www.socsci.mcmaster.ca/jfox

Chris Handorf wrote:
> 
> How does one remove a column from a data frame when the name of
> the column to remove is stored in a variable?
> 
> For Example:
> 
> colname <- "LOT"
> 
> newdf <- subset(olddf,select = - colname)
> 
> The above statement will give an error, but thats what I'm trying to
> accomplish.
> 
> If I had used:
> 
> newdf <- subset(olddf,select = - LOT)
> 
> then it would have worked, but as I said the column name is stored in a
> variable
> so I can't just enter it explicity.
What about
 subset(olddf, select= -get(colname))
or
 olddf[, names(olddf) != colname]

Uwe Ligges

> df <- data.frame(a=1, b=2, c=3)
 > df1 <- data.frame(a=1, b=2, c=3)
 > df1[,!is.element(names(df1), "b")]
   a c
1 1 3

Spencer Graves

Chris Handorf wrote:
> How does one remove a column from a data frame when the name of
> the column to remove is stored in a variable?
> 
> For Example:
> 
> colname <- "LOT"
> 
> newdf <- subset(olddf,select = - colname)
> 
> The above statement will give an error, but thats what I'm trying to 
> accomplish.
> 
> If I had used:
> 
> newdf <- subset(olddf,select = - LOT)
> 
> then it would have worked, but as I said the column name is stored in a 
> variable
> so I can't just enter it explicity.
> 
> Thanks.
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help