R help - Aug 2009 - When factor is better than other types, such as vector and frame?

Hi,

It is easy to understand the types vector and frame.

But I am wondering why the type factor is designed in R. What is the
advantage of factor compare with other data types in R? Can somebody
give an example in which case the type factor is much better than
other data types?

Regards,
Peng

Peng Yu schreef:
> Hi,
>
> It is easy to understand the types vector and frame.
>
> But I am wondering why the type factor is designed in R. What is the
> advantage of factor compare with other data types in R? Can somebody
> give an example in which case the type factor is much better than
> other data types?
>
> Regards,
> Peng
>
> ______________________________________________
> 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.Hi, 
>   
Hi,

Factor is better when the  variable is categorical, such as 'Forest', 
'Woodland' etc. When performing for example an lm() the categorical 
variables have to be a factor in order for R to recognize it in that way.

cheers,
Paul

On Sat, 22-Aug-2009 at 10:00PM -0500, Peng Yu wrote:

|> Hi,
|> 
|> It is easy to understand the types vector and frame.

Types of what?  Class of object?  Doesn't seem likely.  What do you
mean by frame?  It's a function, and a vector can be a factor,
numeric, logical or character (and probably a few others).

I really don't know what your question is about.  Maybe someone else
can guess what it is you want to know.

|> 
|> But I am wondering why the type factor is designed in R. What is
|> the advantage of factor compare with other data types in R? Can
|> somebody give an example in which case the type factor is much
|> better than other data types?




-- 
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   ___    Patrick Connolly   
 {~._.~}                   Great minds discuss ideas    
 _( Y )_  	         Average minds discuss events 
(:_~*~_:)                  Small minds discuss people  
 (_)-(_)  	                      ..... Eleanor Roosevelt
	  
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Hi

r-help-bounces at r-project.org napsal dne 23.08.2009 05:00:11:
> Hi,
> 
> It is easy to understand the types vector and frame.
> 
> But I am wondering why the type factor is designed in R. What is the
> advantage of factor compare with other data types in R? Can somebody
> give an example in which case the type factor is much better than
> other data types?
Although your expressions do not correspond much with naming conventions 
in R, usage of factor is sometimes preferable to character values.

consider e.g.

set.seed(111)
df<-data.frame(1:5, fac=sample(letters[1:2], 5, replace=T))
plot(df[,1], pch=as.numeric(df[,2]))
df[,2]<-as.character(df[,2])
plot(df[,1], pch=as.numeric(df[,2]))

Warning message:
In plot.xy(xy, type, ...) : NAs introduced by coercion

Another advantage is simple and straightforward manipulation with levels.

levels(df[,2])<-c("yes", "no")
> df
  X1.5 fac
1    1  no
2    2  no
3    3 yes
4    4  no
5    5 yes

together with easy ordering option of levels and subsequent plotting order 
in boxplots and similar.
> factor(df$fac, levels=levels(df$fac))
[1] no  no  yes no  yes
Levels: yes no
> factor(df$fac, levels=levels(df$fac)[2:1])
[1] no  no  yes no  yes
Levels: no yes

You need to get used to some features which are sometimes surprising but 
has a reason like levels persisting in subset.
> str(df[df$fac=="no",])
'data.frame':   3 obs. of  2 variables:
 $ X1.5: int  1 2 4
 $ fac : Factor w/ 2 levels "yes","no": 2 2
2
>
Regards
Petr


> 
> Regards,
> Peng
> 
> ______________________________________________
> 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.