[R] tapply changing order of factor levels?

[Alain Guillet]

Hi,

I meant that your problem occured because the levels of mylevels are not 
ordered whereas tapply uses the ordered levels for printing. If you 
order them (look under), you can see the results of the tapply has the 
same order as the levels of myfactor

 >mydata<-c("IN0020020155","IN0019800021","IN0020020064","IN0020020155","IN0019800021","IN0019800021","IN0020020064","IN0020020064","IN0019800021")
 > mylevels<-c("IN0020020155","IN0019800021","IN0020020064")
 > myfactor<-factor(mydata,levels=mylevels)
 > myfactor
[1] IN0020020155 IN0019800021 IN0020020064 IN0020020155 IN0019800021
[6] IN0019800021 IN0020020064 IN0020020064 IN0019800021
Levels: IN0020020155 IN0019800021 IN0020020064
 > levels(myfactor) <- sort(mylevels)
 > myfactor
[1] IN0019800021 IN0020020064 IN0020020155 IN0019800021 IN0020020064
[6] IN0020020064 IN0020020155 IN0020020155 IN0020020064
Levels: IN0019800021 IN0020020064 IN0020020155
 > tapply(myfactor,mydata,length)
IN0019800021 IN0020020064 IN0020020155
           4            3            2


Chirantan Kundu wrote:
> Hi Alain,
>
> I tried levels(myfactor) as you suggested.
>
> > levels(myfactor)
> [1] "IN0020020155" "IN0019800021" "IN0020020064"
>
> The order is preserved, no alphanumerical sorting done here.
> Regards.
>
> On Wed, May 6, 2009 at 7:35 PM, Alain Guillet 
> <alain.guillet at uclouvain.be <mailto:alain.guillet at uclouvain.be>> wrote:
>
>     Hi,
>
>     I don't believe the problem is related to tapply. I would say it
>     is because of the factor. In fact, the order of a factor is given
>     by the alphanumerical order of his levels. You can see it with
>     levels(myfactor).
>     I you want to change the order, redefine the levels of myfactor
>     with the expected order or use the function ordered.
>
>     Alain
>
>
>     Chirantan Kundu wrote:
>
>         Hi,
>
>         Does tapply change the order when applied on a factor? Below
>         is the code I
>         tried.
>
>          
>
>             mylevels<-c("IN0020020155","IN0019800021","IN0020020064")
>
>                
>
>         mydata<-c("IN0020020155","IN0019800021","IN0020020064","IN0020020155","IN0019800021","IN0019800021","IN0020020064","IN0020020064","IN0019800021")
>          
>
>             myfactor<-factor(mydata,levels=mylevels)
>             myfactor
>                
>
>         [1] IN0020020155 IN0019800021 IN0020020064 IN0020020155
>         IN0019800021
>         IN0019800021 IN0020020064 IN0020020064 IN0019800021
>         Levels: IN0020020155 IN0019800021 IN0020020064
>          
>
>             summary(myfactor)
>                
>
>         IN0020020155 IN0019800021 IN0020020064
>                   2            4            3
>
>         # Everything fine upto this point. The order of levels is
>         maintained as it
>         is.
>
>          
>
>             mysummary<-tapply(myfactor,mydata,length)
>             mysummary
>                
>
>         IN0019800021 IN0020020064 IN0020020155
>                   4            3            2
>
>         # Now the order has changed.
>
>         Is this the expected behavior? Any idea on how to avoid the
>         change in order?
>
>         Regards,
>         Chirantan
>
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>          
>
>
>     -- 
>     Alain Guillet
>     Statistician and Computer Scientist
>
>     SMCS - Institut de statistique - Université catholique de Louvain
>     Bureau d.126
>     Voie du Roman Pays, 20
>     B-1348 Louvain-la-Neuve
>     Belgium
>
>     tel: +32 10 47 30 50
>
>
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>
>
>   

-- 
Alain Guillet
Statistician and Computer Scientist

SMCS - Institut de statistique - Université catholique de Louvain
Bureau d.126
Voie du Roman Pays, 20
B-1348 Louvain-la-Neuve
Belgium

tel: +32 10 47 30 50