[R] subset drop unused levels

[Spencer Graves]

      "an assignment to a square bracket" implies that the object 
already exists and gives an error if it does not.  Consider the following: 

 > a[] <- 1:3
Error: Object "a" not found
 > a <- 1:2
 > a[] <- 1:3
Warning message:
number of items to replace is not a multiple of replacement length
 >

      hope this helps.  spencer graves

merser at tiscali.dk wrote:

>thank you
>sorry, but i missed that thread
>your solution works (of cause)
>
>hopefully the code and not the documentation will be corrected as the drop
>argument comes very convenient or maybe as a new option:  drop.unused.levels=T
> 
>regards soren
>
>btw 
>how do i interpret an assigment to a square bracket?
>d2[] <- lapply(d2, function(x) if (is.factor(x)) factor(x) else x) 
>
>
>----- Original Message ----- 
>From: "Peter Dalgaard" <p.dalgaard at biostat.ku.dk>
>To: "Søren Merser" <merser at image.dk>
>Cc: "R - help" <r-help at stat.math.ethz.ch>
>Sent: Sunday, June 27, 2004 11:38 AM
>Subject: Re: [R] subset drop unused levels
>
>
>  
>
>>Søren Merser <merser at image.dk> writes:
>>
>>    
>>
>>>hi there
>>>
>>>tried to use subset with drop=TRUE, but all the 'old' levels are preserved,
>>>i.e. when calling e.g. ftable a lot of zeros are displayed
>>>
>>>      
>>>
>>>>x<-subset(LREG,  (kir=='AA' | kir=='BB') & (type=='t1' | otype=='t2'),
>>>>        
>>>>
>>>drop=TRUE, select=c(event, kir, type))
>>>      
>>>
>>>>ftable(x)
>>>>        
>>>>
>>>i explicit have to call factor like
>>>      
>>>
>>>>ftable(event~factor(kir)+factor(type))
>>>>        
>>>>
>>>any hints?
>>>      
>>>
>>Yes, the drop argument is misdocumented. It actually does the same as
>>the drop argument to [.data.frame. It was on this very list just
>>eleven days ago, see e.g. the below ref., including what to do if you
>>really want to get rid of unused levels
>>
>>http://www.mail-archive.com/r-help@stat.math.ethz.ch/msg22459.html
>>
>>(yet another interface to the archives...)
>>
>>-- 
>>   O__  ---- Peter Dalgaard             Blegdamsvej 3  
>>  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
>> (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
>>~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
>>
>>______________________________________________
>>R-help at stat.math.ethz.ch mailing list
>>https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>>PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
>>
>>    
>>
>
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