R help - Sep 2005 - How to exclude a level from a factor

Hi,

I could not use 'exlcude=' option in factor()
to exclude a level from a existing factor.

x is a factor:
> x
[1] a b c
Levels: a b c
> factor(x,exclude="c")
[1] a b c
Levels: a b c
Warning message:
NAs introduced by coercion

However, "c" is not coded as NA.

The following does not work either:
>
factor(x,exclude=factor("c",levels=c("a","b","c")))
[1] a b c
Levels: a b c


What's wrong with my codes?

Thanks for any help

Qiong Yang

Qiong Yang wrote:
> Hi,
> 
> I could not use 'exlcude=' option in factor()
> to exclude a level from a existing factor.
> 
> x is a factor:
> 
> 
>>x
> 
> [1] a b c
> Levels: a b c
> 
> 
>>factor(x,exclude="c")
> 
> [1] a b c
> Levels: a b c
> Warning message:
> NAs introduced by coercion
> 
> However, "c" is not coded as NA.
> 
> The following does not work either:
> 
> 
>>factor(x,exclude=factor("c",levels=c("a","b","c")))
> 
> [1] a b c
> Levels: a b c
> 
> 
> What's wrong with my codes?
> 

I think you want:

x <- factor(letters[1:3])
factor(as.character(x), exclude = "c")

HTH,
--sundar

Qiong Yang wrote:
> Hi,
> 
> I could not use 'exlcude=' option in factor()
> to exclude a level from a existing factor.
> 
> x is a factor:
> 
> 
>>x
> 
> [1] a b c
> Levels: a b c
> 
> 
>>factor(x,exclude="c")
> 
> [1] a b c
> Levels: a b c
> Warning message:
> NAs introduced by coercion
> 
> However, "c" is not coded as NA.
> 
> The following does not work either:
> 
> 
>>factor(x,exclude=factor("c",levels=c("a","b","c")))
> 
> [1] a b c
> Levels: a b c
> 
> 
> What's wrong with my codes?

  factor(x, levels=letters[1:2])

Uwe Ligges
> Thanks for any help
> 
> Qiong Yang
> 
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