R Under development (unstable) (2024-03-19 r86153 ucrt) -- "Unsuffered Consequences"
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> 
> ## check that stringsAsFactors fixes the string levels problem
> data(api, package = "survey")
> des <- survey::svydesign(id = ~dnum, weights = ~pw, data = apiclus1, fpc = ~fpc)
> est0 <-
+   survey::svyby(design=des, formula=~cname, by=~both, FUN=survey::svymean, keep.var=TRUE, stringsAsFactors=TRUE) 
> 
> stopifnot(isTRUE(all(dim(est0)==c(2,23))))
> 
> proc.time()
   user  system elapsed 
   1.68    0.23    1.90