scale_*_discrete(drop = FALSE) changed behaviour/stopped working in version < 3.5.0

[markus-schaffer]

The behaviour of scale_*_discrete(drop = FALSE) stopped working/changed its behaviour for ggplot2 < 3.5.0 (without that I was able to find information about it in the changelog) . The legend does not longer show the colour/symbols for levels without data.

ggplot2 version 3.5.1

library(ggplot2)

df <- data.frame(
  x = 1:5, 
  y = rep(1,5),
  z = factor(c(1,1,3,1,1), levels = c("1","2","3","4","5"))
)
df$z
#> [1] 1 1 3 1 1
#> Levels: 1 2 3 4 5

ggplot(df, aes(x, y, fill = z)) +
  geom_tile()+
  scale_fill_discrete(drop = FALSE)

ggplot(df, aes(x, y, color = z)) +
  geom_point()+
  scale_color_discrete(drop = FALSE)

sessionInfo()
#> R version 4.4.1 (2024-06-14 ucrt)
#> Platform: x86_64-w64-mingw32/x64
#> Running under: Windows 10 x64 (build 19045)
#> 
#> Matrix products: default
#> 
#> 
#> locale:
#> [1] LC_COLLATE=Danish_Denmark.utf8  LC_CTYPE=Danish_Denmark.utf8   
#> [3] LC_MONETARY=Danish_Denmark.utf8 LC_NUMERIC=C                   
#> [5] LC_TIME=Danish_Denmark.utf8    
#> 
#> time zone: Europe/Copenhagen
#> tzcode source: internal
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] ggplot2_3.5.1
#> 
#> loaded via a namespace (and not attached):
#>  [1] vctrs_0.6.5       cli_3.6.3         knitr_1.47        rlang_1.1.4      
#>  [5] xfun_0.45         purrr_1.0.2       styler_1.10.3     generics_0.1.3   
#>  [9] labeling_0.4.3    glue_1.7.0        colorspace_2.1-0  htmltools_0.5.8.1
#> [13] fansi_1.0.6       scales_1.3.0      rmarkdown_2.27    R.cache_0.16.0   
#> [17] grid_4.4.1        tibble_3.2.1      munsell_0.5.1     evaluate_0.24.0  
#> [21] fastmap_1.2.0     yaml_2.3.8        lifecycle_1.0.4   compiler_4.4.1   
#> [25] dplyr_1.1.4       fs_1.6.4          pkgconfig_2.0.3   rstudioapi_0.16.0
#> [29] R.oo_1.26.0       farver_2.1.2      R.utils_2.12.3    digest_0.6.35    
#> [33] R6_2.5.1          tidyselect_1.2.1  utf8_1.2.4        reprex_2.1.0     
#> [37] pillar_1.9.0      magrittr_2.0.3    R.methodsS3_1.8.2 tools_4.4.1      
#> [41] withr_3.0.0       gtable_0.3.5

ggplot2 version 3.4.4

library(ggplot2)

df <- data.frame(
  x = 1:5, 
  y = rep(1,5),
  z = factor(c(1,1,3,1,1), levels = c("1","2","3","4","5"))
)
df$z
#> [1] 1 1 3 1 1
#> Levels: 1 2 3 4 5

ggplot(df, aes(x, y, fill = z)) +
  geom_tile()+
  scale_fill_discrete(drop = FALSE)

ggplot(df, aes(x, y, color = z)) +
  geom_point()+
  scale_color_discrete(drop = FALSE)

sessionInfo()
#> R version 4.4.1 (2024-06-14 ucrt)
#> Platform: x86_64-w64-mingw32/x64
#> Running under: Windows 10 x64 (build 19045)
#> 
#> Matrix products: default
#> 
#> 
#> locale:
#> [1] LC_COLLATE=Danish_Denmark.utf8  LC_CTYPE=Danish_Denmark.utf8   
#> [3] LC_MONETARY=Danish_Denmark.utf8 LC_NUMERIC=C                   
#> [5] LC_TIME=Danish_Denmark.utf8    
#> 
#> time zone: Europe/Copenhagen
#> tzcode source: internal
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] ggplot2_3.4.4
#> 
#> loaded via a namespace (and not attached):
#>  [1] vctrs_0.6.5       cli_3.6.3         knitr_1.47        rlang_1.1.4      
#>  [5] xfun_0.45         purrr_1.0.2       styler_1.10.3     generics_0.1.3   
#>  [9] labeling_0.4.3    glue_1.7.0        colorspace_2.1-0  htmltools_0.5.8.1
#> [13] fansi_1.0.6       scales_1.3.0      rmarkdown_2.27    R.cache_0.16.0   
#> [17] grid_4.4.1        tibble_3.2.1      munsell_0.5.1     evaluate_0.24.0  
#> [21] fastmap_1.2.0     yaml_2.3.8        lifecycle_1.0.4   compiler_4.4.1   
#> [25] dplyr_1.1.4       fs_1.6.4          pkgconfig_2.0.3   rstudioapi_0.16.0
#> [29] R.oo_1.26.0       farver_2.1.2      R.utils_2.12.3    digest_0.6.35    
#> [33] R6_2.5.1          tidyselect_1.2.1  utf8_1.2.4        reprex_2.1.0     
#> [37] pillar_1.9.0      magrittr_2.0.3    R.methodsS3_1.8.2 tools_4.4.1      
#> [41] withr_3.0.0       gtable_0.3.5

^{Created on 2024-07-01 with reprex v2.1.0}

[teunbrand]

This issue is a duplicate of #5728.
In short, you'd need to use show.legend = TRUE if you want to display keys for data that isn't present in the legend.