R Under development (unstable) (2024-03-07 r86063 ucrt) -- "Unsuffered Consequences"
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> library(survey)
Loading required package: grid
Loading required package: Matrix
Loading required package: survival

Attaching package: 'survey'

The following object is masked from 'package:graphics':

    dotchart

> 
> # don't throw an error on domains of size 1, just return NA
> input <- mtcars
> input$carb <- factor(input$carb)
> design <- svydesign(ids = ~0, weights = NULL, data = input)
> svyby(
+   ~mpg,
+   ~carb,
+   design,
+   svyvar
+ )
  carb      mpg         se
1    1 36.01619 11.2823286
2    2 29.94444  9.0030898
3    3  1.11000  0.4604066
4    4 15.29656  4.3174617
6    6       NA         NA
8    8       NA         NA
> 
> 
> ## same n with na.rm=TRUE as subset(, !is.na)
> input$mpg[1]<-NA
> design <- svydesign(ids = ~0, weights = NULL, data = input)
> stopifnot(all.equal(svyvar(~mpg, design, na.rm=TRUE),
+           svyvar(~mpg, subset(design, !is.na(mpg)))))
> 
> proc.time()
   user  system elapsed 
   1.10    0.06    1.15