dydx() with change = "iqr" not working as expected

[lang-benjamin]

• [X] a possible bug
• [ ] a question about package functionality
• [ ] a suggested code or documentation change, improvement to the code, or feature request

I think option change = "iqr" in function dydx() does not work properly. For example:

library(margins)
fm <- lm(mpg ~ hp, data = mtcars)
dydx(mtcars, fm, "hp", change = "iqr")
#>      dydx_hp
#> 1  -5.731175
#> 2  -5.731175
#> 3  -5.731175
#> 4  -5.731175
#> 5  -5.731175
#> 6  -5.731175
#> 7  -5.731175
#> 8  -5.731175
#> 9  -5.731175
#> 10 -5.731175
#> 11 -5.731175
#> 12 -5.731175
#> 13 -5.731175
#> 14 -5.731175
#> 15 -5.731175
#> 16 -5.731175
#> 17 -5.731175
#> 18 -5.731175
#> 19 -5.731175
#> 20 -5.731175
#> 21 -5.731175
#> 22 -5.731175
#> 23 -5.731175
#> 24 -5.731175
#> 25 -5.731175
#> 26 -5.731175
#> 27 -5.731175
#> 28 -5.731175
#> 29 -5.731175
#> 30 -5.731175
#> 31 -5.731175
#> 32 -5.731175
# I would have expected the same result as in
dydx(mtcars, fm, "hp", change = c(quantile(mtcars$hp, 1/4), quantile(mtcars$hp, 3/4)))
#>      dydx_hp
#> 1  -5.697061
#> 2  -5.697061
#> 3  -5.697061
#> 4  -5.697061
#> 5  -5.697061
#> 6  -5.697061
#> 7  -5.697061
#> 8  -5.697061
#> 9  -5.697061
#> 10 -5.697061
#> 11 -5.697061
#> 12 -5.697061
#> 13 -5.697061
#> 14 -5.697061
#> 15 -5.697061
#> 16 -5.697061
#> 17 -5.697061
#> 18 -5.697061
#> 19 -5.697061
#> 20 -5.697061
#> 21 -5.697061
#> 22 -5.697061
#> 23 -5.697061
#> 24 -5.697061
#> 25 -5.697061
#> 26 -5.697061
#> 27 -5.697061
#> 28 -5.697061
#> 29 -5.697061
#> 30 -5.697061
#> 31 -5.697061
#> 32 -5.697061

^{Created on 2020-06-21 by the reprex package (v0.3.0)}

Session info

sessionInfo()
#> R version 4.0.0 (2020-04-24)
#> Platform: x86_64-apple-darwin17.0 (64-bit)
#> Running under: macOS High Sierra 10.13.6
#> 
#> Matrix products: default
#> BLAS:   /Library/Frameworks/R.framework/Versions/4.0/Resources/lib/libRblas.dylib
#> LAPACK: /Library/Frameworks/R.framework/Versions/4.0/Resources/lib/libRlapack.dylib
#> 
#> locale:
#> [1] de_DE.UTF-8/de_DE.UTF-8/de_DE.UTF-8/C/de_DE.UTF-8/de_DE.UTF-8
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] margins_0.3.23
#> 
#> loaded via a namespace (and not attached):
#>  [1] Rcpp_1.0.4.6      digest_0.6.25     MASS_7.3-51.6     magrittr_1.5     
#>  [5] evaluate_0.14     highr_0.8         rlang_0.4.6       stringi_1.4.6    
#>  [9] data.table_1.12.8 rmarkdown_2.1     prediction_0.3.14 tools_4.0.0      
#> [13] stringr_1.4.0     xfun_0.14         yaml_2.2.1        compiler_4.0.0   
#> [17] htmltools_0.4.0   knitr_1.28

[leeper]

Thanks. This looks like it is due to the internal use of fivenum() returning integers rather than numeric quantiles. I'll switch out the implementation as that's not correct.