One more note. There is actually a valid reason to use `levels<-`, and that is
to change the spelling of the levels while maintaining the existing order.
> tmp <- factor(c("mm", "cm", "dm", "m", "km"))
> tmp
[1] mm cm dm m km
Levels: cm dm km m mm
> levels(tmp) <- c("centimeter","decimeter","kilometer","meter","millimeter")
> tmp
[1] millimeter centimeter decimeter meter kilometer
5 Levels: centimeter decimeter kilometer ... millimeter
> levels(tmp)
[1] "centimeter" "decimeter" "kilometer" "meter"
[5] "millimeter"
>
Rich
On Fri, Jun 5, 2015 at 4:47 AM, Gerrit Eichner
<gerrit.eich...@math.uni-giessen.de> wrote:
> Hello, everyone,
>
> aside from Rolf's hint (and Richard's warning!) you could also consider
> relevel():
>
> viagraData$dose <- relevel( viagraData$dose, ref = "placebo")
>
> Hth -- Gerrit
>
>
> On Fri, 5 Jun 2015, Rolf Turner wrote:
>
>> On 05/06/15 11:08, Jim Lemon wrote:
>>>
>>> Hi James,
>>> You can change the order of levels like this:
>>>
>>> levels(viagraData$dose)<-c("placebo","low dose","high dose")
>>
>>
>> <SNIP>
>>
>> As Richard Heiberger has pointed out, this is wrong.
>>
>> What *does* work is:
>>
>> viagraData$dose)<-factor(viagraData$dose,
>> levels=c("placebo","low dose","high dose")
>>
>> This is a trap into which many a Young Player (including my very good
>> self) has fallen.
>>
>> cheers,
>>
>> Rolf Turner
>>
>>
>>
>> --
>> Technical Editor ANZJS
>> Department of Statistics
>> University of Auckland
>> Phone: +64-9-373-7599 ext. 88276
>>
>> ______________________________________________
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>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>
> ______________________________________________
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
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