Warn when bootstraps returns the apparent

[mikemahoney218]

Fixes #356

library(rsample)

bootstraps(mtcars[1, ])
#> Warning in bootstraps(mtcars[1, ]): Some assessment sets contained zero rows.
#> # Bootstrap sampling 
#> # A tibble: 25 × 2
#>    splits        id         
#>    <list>        <chr>      
#>  1 <split [1/0]> Bootstrap01
#>  2 <split [1/0]> Bootstrap02
#>  3 <split [1/0]> Bootstrap03
#>  4 <split [1/0]> Bootstrap04
#>  5 <split [1/0]> Bootstrap05
#>  6 <split [1/0]> Bootstrap06
#>  7 <split [1/0]> Bootstrap07
#>  8 <split [1/0]> Bootstrap08
#>  9 <split [1/0]> Bootstrap09
#> 10 <split [1/0]> Bootstrap10
#> # … with 15 more rows
#> # ℹ Use `print(n = ...)` to see more rows
group_bootstraps(mtcars, cyl)
#> Warning in group_bootstraps(mtcars, cyl): Some assessment sets contained zero rows.
#> ℹ Consider using a non-grouped resampling method.
#> # Group bootstrap sampling 
#> # A tibble: 25 × 2
#>    splits          id         
#>    <list>          <chr>      
#>  1 <split [36/7]>  Bootstrap01
#>  2 <split [35/11]> Bootstrap02
#>  3 <split [36/7]>  Bootstrap03
#>  4 <split [35/11]> Bootstrap04
#>  5 <split [33/21]> Bootstrap05
#>  6 <split [39/7]>  Bootstrap06
#>  7 <split [28/11]> Bootstrap07
#>  8 <split [29/14]> Bootstrap08
#>  9 <split [29/14]> Bootstrap09
#> 10 <split [36/7]>  Bootstrap10
#> # … with 15 more rows
#> # ℹ Use `print(n = ...)` to see more rows

^{Created on 2022-08-08 by the reprex package (v2.0.1)}

[mikemahoney218]

GitHub really hates when I request two reviews 🤦

[juliasilge]

Looks great! 🙌

[github-actions]

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