[R] ordering levels

(Ted Harding) Ted.Harding at nessie.mcc.ac.uk
Wed Dec 22 13:37:30 CET 2004

On 22-Dec-04 Anne wrote:
> Hello!
> I would like to know if there is a simple way to reorder levels
> of a given factor.Let's say  that the  vector
> testf<-factor(c("red","red","red","blue","blue","white")) 
>   levels(testf)  : blue red white 
> should have reordered levels  such as 
>  levels(testf)  : red blue  white 
>  (this is for presentation purposes)
> I guess I'm looking for a generalized version of "relevel"...

Hi Anne,

Look at ?factor and note the default

   levels = sort(unique.default(x), na.last = TRUE)


   factor(x, levels = sort(unique.default(x), na.last = TRUE),
          labels = levels, exclude = NA, ordered = is.ordered(x))

You can change the order of levels by changing the "levels = ...",
as in

> factor(c("1.2nd","2.1st","3.4th","4.3rd"))
[1] 1.2nd 2.1st 3.4th 4.3rd
Levels: 1.2nd 2.1st 3.4th 4.3rd

> factor(c("1.2nd","2.1st","3.4th","4.3rd"),
[1] 1.2nd 2.1st 3.4th 4.3rd
Levels: 2.1st 1.2nd 4.3rd 3.4th

Hoping this helps,

E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
Fax-to-email: +44 (0)870 094 0861  [NB: New number!]
Date: 22-Dec-04                                       Time: 12:37:30
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