R help - Sep 2004 - Removing constants from a data frame

Suppose I have

x<-data.frame(v1=1:4, v2=c(2,4,NA,7), v3=rep(1,4),
     v4=LETTERS[1:4],v5=rep('Z',4))

or a much larger frame, and I wish to test for and remove the constant
numeric columns.

I made:

   is.constant<-function(x){identical(min(x),max(x))}

and
   apply(x,2,is.constant) # Works for numerics
   x[,-which(apply(x,2,is.constant))]

I'd really like to be able to delete the constant columns without losing
my non-numerics.  Ignoring the character columns would be OK.

Any suggestions?

Dave
-- 
 Dave Forrest
 drf at vims.edu                                    (804)684-7900w
 drf5n at maplepark.com                             (804)642-0662h
                                   http://maplepark.com/~drf5n/

David Forrest wrote:
>Suppose I have
>
>x<-data.frame(v1=1:4, v2=c(2,4,NA,7), v3=rep(1,4),
>     v4=LETTERS[1:4],v5=rep('Z',4))
>
>or a much larger frame, and I wish to test for and remove the constant
>numeric columns.
>
>I made:
>
>   is.constant<-function(x){identical(min(x),max(x))}
>
>and
>   apply(x,2,is.constant) # Works for numerics
>   x[,-which(apply(x,2,is.constant))]
>
>I'd really like to be able to delete the constant columns without losing
>my non-numerics.  Ignoring the character columns would be OK.
>
>Any suggestions?
>
>Dave
>  
>
what about defing is.constant as
is.constant <-  function(x) {
                     if (is.numeric(x))  identical(min(x), max(x)) else 
FALSE }

Kjetil halvorsen

-- 

Kjetil Halvorsen.

Peace is the most effective weapon of mass construction.
               --  Mahdi Elmandjra

On 17 Sep 2004 at 19:17, Kjetil Brinchmann Halvorsen wrote:
> David Forrest wrote:
> 
> >Suppose I have
> >
> >x<-data.frame(v1=1:4, v2=c(2,4,NA,7), v3=rep(1,4),
> >     v4=LETTERS[1:4],v5=rep('Z',4))
> >
> >or a much larger frame, and I wish to test for and remove the
> >constant numeric columns.
> >
> >I made:
> >
> >   is.constant<-function(x){identical(min(x),max(x))}
> >
> >and
> >   apply(x,2,is.constant) # Works for numerics
> >   x[,-which(apply(x,2,is.constant))]
> >
> >I'd really like to be able to delete the constant columns without
> >losing my non-numerics.  Ignoring the character columns would be OK.
> >
> >Any suggestions?
> >
> >Dave
> >  
> >
> what about defing is.constant as
> is.constant <-  function(x) {
>                      if (is.numeric(x))  identical(min(x), max(x))
>                      else 
> FALSE }
> 
> Kjetil halvorsen
Hi
Maybe this will do it
> fff<-function(a) if(is.numeric(a)) diff(range(a, na.rm=T))==0 else FALSE
> x[,!mapply(fff,x)]
  v1 v2 v4 v5
1  1  2  A  Z
2  2  4  B  Z
3  3 NA  C  Z
4  4  7  D  Z
>
Cheers
Petr


> 
> -- 
> 
> Kjetil Halvorsen.
> 
> Peace is the most effective weapon of mass construction.
>                --  Mahdi Elmandjra
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
Petr Pikal
petr.pikal at precheza.cz

> From: Kjetil Brinchmann Halvorsen
> 
> David Forrest wrote:
> 
> >Suppose I have
> >
> >x<-data.frame(v1=1:4, v2=c(2,4,NA,7), v3=rep(1,4),
> >     v4=LETTERS[1:4],v5=rep('Z',4))
> >
> >or a much larger frame, and I wish to test for and remove 
> the constant
> >numeric columns.
> >
> >I made:
> >
> >   is.constant<-function(x){identical(min(x),max(x))}
> >
> >and
> >   apply(x,2,is.constant) # Works for numerics
> >   x[,-which(apply(x,2,is.constant))]
> >
> >I'd really like to be able to delete the constant columns 
> without losing
> >my non-numerics.  Ignoring the character columns would be OK.
> >
> >Any suggestions?
> >
> >Dave
> >  
> >
> what about defing is.constant as
> is.constant <-  function(x) {
>                      if (is.numeric(x))  identical(min(x), 
> max(x)) else 
> FALSE }
identical() is probably not the safest thing to use:
> x <- c(1, 2, NA)
> is.constant(x)
[1] TRUE

For data such as c(1, 1, 1, NA), I should think the safest answer should be
NA, because one really doesn't know whether that last number is 1 or not.

Andy
 
> -- 
> Kjetil Halvorsen.
> 
> Peace is the most effective weapon of mass construction.
>                --  Mahdi Elmandjra
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
> 
>