R help - Dec 2009 - how to combine multiple indicator variables in a single factor

Say I have a dataframe like this:

df <- data.frame(cbind(c(1,0,0,1),c(0,1,0,0),c(0,0,1,0)))

names(df) <- c('a','b','c')

I would like to create a factor in a new column, where the factor values are
taken from the column names, like this:
> df2
  a b c f
1 1 0 0 a
2 0 1 0 b
3 0 0 1 c
4 1 0 0 a

How would I do this?  Thanks,

Dan

Daniel Nordlund
Bothell, WA USA

you can try:

df$f<-names(df)[apply(df,1,function(x) which(x==1))]

Ehud

On Fri, Dec 18, 2009 at 10:48 PM, Daniel Nordlund
<djnordlund at verizon.net> wrote:
> Say I have a dataframe like this:
>
> df <- data.frame(cbind(c(1,0,0,1),c(0,1,0,0),c(0,0,1,0)))
>
> names(df) <- c('a','b','c')
>
> I would like to create a factor in a new column, where the factor values
are taken from the column names, like this:
>
>> df2
> ?a b c f
> 1 1 0 0 a
> 2 0 1 0 b
> 3 0 0 1 c
> 4 1 0 0 a
>
> How would I do this? ?Thanks,
>
> Dan
>
> Daniel Nordlund
> Bothell, WA USA
>
> ______________________________________________
> 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.
>

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Daniel Nordlund
> Sent: Friday, December 18, 2009 12:49 PM
> To: r-help at r-project.org
> Subject: [R] how to combine multiple indicator variables in a 
> single factor
> 
> Say I have a dataframe like this:
> 
> df <- data.frame(cbind(c(1,0,0,1),c(0,1,0,0),c(0,0,1,0)))
> 
> names(df) <- c('a','b','c')
> 
> I would like to create a factor in a new column, where the 
> factor values are taken from the column names, like this:
> 
> > df2
>   a b c f
> 1 1 0 0 a
> 2 0 1 0 b
> 3 0 0 1 c
> 4 1 0 0 a
> 
> How would I do this?  Thanks,
One possibility is
   > df$f <- factor(df$a + df$b*2 + df$c*3, labels=names(df)[1:3])
   > df
     a b c f
   1 1 0 0 a
   2 0 1 0 b
   3 0 0 1 c
   4 1 0 0 a


Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  
> 
> Dan
> 
> Daniel Nordlund
> Bothell, WA USA
> 
> ______________________________________________
> 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.
>