[Rd] Relevel confusing with numeric value

[peter dalgaard]

In a word, no. It is behaving as documented and adding a warning would just confuse others who have been using the feature as intended. 

This belongs in the same bin as "as.integer(f) vs as.integer(as.character(f))" and "x[f] vs. x[as.character(f)]"

-pd


> On 2 Oct 2018, at 17:18 , Emil Bode <emil.bode using dans.knaw.nl> wrote:
> 
> Something that bit me:
> The function relevel takes a factor, and a reference level to be promoted to the first place.
> If “ref” is a character this level is promoted, if it’s a numeric the “ref”-th level is promoted.
> Which turns out to be very confusing if you have factor with numeric values (e.g. when reading in a csv with some dirty numeric columns and stringsAsFactors TRUE)
> For example:
> 
> set.seed(1)
> test <- data.frame(n=sample(c(1:100, letters[1:10]), size=90))
> test$n <- relevel(test$n, 50)
> print(levels(test$n))
> 
> gives “62” as the first level.
> 
> Could we make something like this an error, or at least issue a warning?
> Also because some other functions automatically coerce, factor(…, levels=1:100) and levels(test$n) <- 1:100 works fine.
> So this is maybe the most confusing: relevel(factor(1:10, levels = -10:20), 15) gives “4” as the first level
> 
> For now I’ve thought of 2 possible implementations, that could be inserted in stats::relevel.factor(), just before is.character(ref):
> 
> if(is.numeric(ref) && ref %in% lev)
>    warning('Provided numeric reference, note that this will promote the ', ref, 'th value, not level with value "', ref, '"!')
> 
> or
> 
> if(is.numeric(ref) && any(!is.na(suppressWarnings(as.numeric(lev)))))
>    warning('Provided numeric reference, note that this will promote the ', ref, 'th value, not level with value "', ref, '"!')
> 
> 
> Best regards,
> Emil Bode
> 
> Data-analyst
> 
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-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
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