[Rd] Getting ordered factor levels from C

Simon Urbanek simon.urbanek at r-project.org
Wed Oct 24 22:16:54 CEST 2012

On Oct 24, 2012, at 2:14 PM, Mark Lilback wrote:

> I'm working on an R package in C and can't seem to get the same level information about a factor that the R console displays.
> If I define a factor as:
> lvls <- factor(c('red','blue','blue','green','red'), c('blue','green','red'), ordered=TRUE)
> When I get the "levels" attribute in C, I get back the the first vector, not the second.

What are you using in C? AFAICS it works just fine:

> f=cfunction(c(foo="factor"), "return getAttrib(foo, R_LevelsSymbol);")
> f(lvls)
[1] "blue"  "green" "red"  


> If I run attr(lvls,"levels") in R, I get back the second vector. There are no attributes besides class and levels, so how do I get the list of levels in the correct order?
> Thanks
> -- 
> Mark Lilback
> West Virginia University Department of Statistics
> mlilback at stat.wvu.edu
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