[R] levels update

[Antje]

Thanks a lot!!!
the "drop" thing was exactly what I was looking for (I already used it some 
time ago but forgot about it).

Thanks to everybody else too.

Antje


Prof Brian Ripley schrieb:
> On Fri, 5 Dec 2008, jim holtman wrote:
> 
>> try this:
>>
>>> df <- data.frame(factor(c("a","a","c","b","b")), c(4,5,6,7,8), 
>>> c(9,1,2,3,4))
>>> names(df) <- c("X1","X2","X3")
>>>
>>> my.sub <- subset(df, X1 == "a" | X1 == "b")
>>> levels(my.sub$X1)
>> [1] "a" "b" "c"
>>> my.sub$X1 <- factor(my.sub$X1)
> 
> I find
> 
> my.sub$X1 <- my.sub$X1[drop=TRUE]
> 
> a lot more self-explanatory.  See ?"[.factor".  However, if you find 
> yourself wanting to do this, ask why you have a factor (rather than a 
> character vector) in the first place.
> 
> 
>>> levels(my.sub$X1)
>> [1] "a" "b"
>>>
>>
>>
>> On Fri, Dec 5, 2008 at 7:50 AM, Antje <niederlein-rstat at yahoo.de> wrote:
>>> Hello,
>>>
>>> I hope this question is not too stupid. I would like to know how to 
>>> update
>>> levels after subsetting data from a data.frame.
>>>
>>> df <- data.frame(factor(c("a","a","c","b","b")), c(4,5,6,7,8), 
>>> c(9,1,2,3,4))
>>> names(df) <- c("X1","X2","X3")
>>>
>>> my.sub <- subset(df, X1 == "a" | X1 == "b")
>>> levels(my.sub$X1)
>>>
>>> # still gives me "a","b","c", though the subset does not contain entries
>>> with "c" anymore
>>>
>>> I guess, the solution is rather simple, but I cannot find it.
>>>
>>> Antje
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide 
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>>
>>
>> -- 
>> Jim Holtman
>> Cincinnati, OH
>> +1 513 646 9390
>>
>> What is the problem that you are trying to solve?
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide 
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>