[R] tapply changing order of factor levels?

[Alain Guillet]

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

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