R help - Nov 2009 - how can I delete those columes with the same element in every row?

e.g.  

a  a b c d e
1 1 1 3 1 1
2 1 2 3 4 5
3 1 3 3 8 3
4 1 4 3 3 5
5 1 1 3 1 1        I want to delete  colume a  and colume c, because they
have the same values in every row, then ,I want to get this data.frame .

b  b d  e
1 1 1  1
2 2 4  5
3 3 8  3
4 4 3  5
5 1 1  1        the following is my code but it's wrong.

rm(list=ls())
a=c(1,1,1,1,1); b=c(1,2,3,4,1); c=c(3,3,3,3,3); d=c(1,4,8,3,1);
e=c(1,5,3,5,1) 
data.f=data.frame(a,b,c,d,e)
origin.data<-data.f
dim.frame=dim(data.f)
rn=dim.frame[1] 
n<-0
for (k in 1:(dim.frame[2]-n)) 
{if (data.f[1,k]==data.f[rn,k]) 
  {data.f<-data.f[,-k]
   n<-n+1
   k<-k-1
   }
}
origin.data
data.f  


how can i modify it and obtain my wanted result.

thank you!
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bbslover wrote:
> 
> e.g.  
> 
> a>   a b c d e
> 1 1 1 3 1 1
> 2 1 2 3 4 5
> 3 1 3 3 8 3
> 4 1 4 3 3 5
> 5 1 1 3 1 1        I want to delete  colume a  and colume c, because they
> have the same values in every row, then ,I want to get this data.frame .
> 
> b>   b d  e
> 1 1 1  1
> 2 2 4  5
> 3 3 8  3
> 4 4 3  5
> 5 1 1  1    
> 
Try this

xdf  <- apply(data.f, 2, function(x) x==x[1])
data.f <- data.f[,!apply(xdf,2,all)]
data.f


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it is perfect?you give me a great help. thanks R and Berend Hasselman, my
friends. but I think I do have more questions to ask. 

thank you!

Berend Hasselman wrote:
> 
> 
> 
> bbslover wrote:
>> 
>> e.g.  
>> 
>> a>>   a b c d e
>> 1 1 1 3 1 1
>> 2 1 2 3 4 5
>> 3 1 3 3 8 3
>> 4 1 4 3 3 5
>> 5 1 1 3 1 1        I want to delete  colume a  and colume c, because
they
>> have the same values in every row, then ,I want to get this data.frame
.
>> 
>> b>>   b d  e
>> 1 1 1  1
>> 2 2 4  5
>> 3 3 8  3
>> 4 4 3  5
>> 5 1 1  1    
>> 
> 
> Try this
> 
> xdf  <- apply(data.f, 2, function(x) x==x[1])
> data.f <- data.f[,!apply(xdf,2,all)]
> data.f
> 
> 
> 
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