[R] Changing an unordered factor into an ordered factor

[David Winsemius]

On Feb 4, 2010, at 5:58 AM, Oliver Gondring wrote:

> Hi Mathew,
>
>> I'm trying to change an unordered factor into an ordered factor:
>> Help
>
>
> it's all about reordering the factor levels, right?

It's hard to tell. You could be correct, but the OP never described  
his reasons for wanting "ordered" factors. The page you offer below  
only describes the "ordering" or "releveling" of the levels in  
_unordered_  factors and does not describe creating or working with  
ordered factors which are of a different class.

Ordered factor have additional methods

 > x <- factor(sample(c("Oppose", "Haven't thought much about this",  
"Favor"), 10, replace=TRUE)  )
 > x
  [1] Oppose                          Favor                            
Oppose
  [4] Favor                           Haven't thought much about this  
Oppose
  [7] Oppose                          Oppose                           
Oppose
[10] Oppose
Levels: Favor Haven't thought much about this Oppose

 > ox <- factor(x, levels=c("Haven't thought much about  
this","Oppose",  "Favor"), ordered=TRUE)
 > ox
  [1] Oppose                          Favor                            
Oppose
  [4] Favor                           Haven't thought much about this  
Oppose
  [7] Oppose                          Oppose                           
Oppose
[10] Oppose
Levels: Haven't thought much about this < Oppose < Favor  # Note the  
difference here.

 > ox[1] < ox[3]
[1] FALSE    #  the < operator is meaningful here

 > x[1] < x[3]
[1] NA
Warning message:
In Ops.factor(x[1], x[3]) : < not meaningful for factors
 >

>
> Have a look at this one:
> http://rwiki.sciviews.org/doku.php?id=tips:data-factors:factors
>
> The third textbox on the page (search for the string: "Reorder factor
> levels") provides a piece of sample code for the task. Should be  
> easy to
> adapt it to your problem.
>
> Oliver
>
> P.S.: Maybe it's not a bad idea to provide a more readable
> transformation of your code next time. What about replacing the whole
> 'V961327' thing by 'x' for example?
>

And maybe some sample data as well?
-- 

David Winsemius, MD
Heritage Laboratories
West Hartford, CT