False alarm regarding factor warning

[mattansb]

Here that cyl column is pre-transformed into a factor, but the warning still remains.

data("mtcars")
mtcars$cyl <- factor(mtcars$cyl)
mod <- rstanarm::stan_glm(mpg ~ cyl + hp * am, data = mtcars, refresh = 0)

marginaleffects::comparisons(mod,
                             variables = "cyl",
                             newdata = data.frame(hp = 100, am = 0)
)
#> Warning: The `cyl` variable is treated as a categorical (factor) variable, but
#>   the original data is of class NULL. It is safer and faster to convert
#>   such variables to factor before fitting the model and calling a
#>   `marginaleffects` function.
#>   
#>   This warning appears once per session.
#>   FALSE
#> 
#>  Contrast Estimate 2.5 % 97.5 %  hp am
#>     6 - 4    -3.96 -7.04 -0.631 100  0
#>     8 - 4    -3.52 -9.15  2.223 100  0
#> 
#> Term: cyl
#> Type:  response 
#> Columns: rowid, term, contrast, estimate, conf.low, conf.high, predicted_lo, predicted_hi, predicted, tmp_idx, hp, am, mpg

^{Created on 2024-09-05 with reprex v2.1.0}

Session info

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[1] CRAN (R 4.3.1) #> V8 4.4.2 2024-02-15 [1] CRAN (R 4.3.3) #> vctrs 0.6.5 2023-12-01 [1] CRAN (R 4.3.2) #> withr 3.0.0 2024-01-16 [1] CRAN (R 4.3.2) #> xfun 0.44 2024-05-15 [1] CRAN (R 4.3.3) #> xtable 1.8-4 2019-04-21 [1] CRAN (R 4.3.1) #> xts 0.13.2 2024-01-21 [1] CRAN (R 4.3.2) #> yaml 2.3.8 2023-12-11 [1] CRAN (R 4.3.2) #> zoo 1.8-12 2023-04-13 [1] CRAN (R 4.3.1) #> #> [1] C:/Users/user/AppData/Local/R/win-library/4.3 #> [2] C:/Program Files/R/R-4.3.2/library #> #> D ── DLL MD5 mismatch, broken installation. #> #> ────────────────────────────────────────────────────────────────────────────── ```

[vincentarelbundock]

Your code is incorrect. The message says that cyl is NULL because it is not a column in the data frame that you supplied to newdata.

Instead of newdata=data.frame(), you should use newdata=datagrid(), which is smart enough to create a grid with the appropriate cyl variable when you don't specify it explicitly.

[mattansb]

🤦‍♂️ Thanks