Viridis scale bar does not work with current "inside" legend methodology

[MartinEarle]

The current method for rendering legends inside the plot does not appear to work with the "viridis" colour scale options. Using this approach results in the scale bar being rendered as points, whereas the depeciated method as expected. Please see the code below for an example. Note that my R is a bit outdated but I updated ggplot for this bug report, hence the warning after calling tidyverse.

library(tidyverse)
#> Warning: package 'ggplot2' was built under R version 4.4.3

#Regular scale, outside of plot area
mtcars %>% 
  ggplot(aes(cyl, mpg, col = hp)) +
  geom_point() +
  scale_colour_viridis_c() 

#Inside scale using current approach
mtcars %>% 
  ggplot(aes(cyl, mpg, col = hp)) +
    geom_point() +
    scale_colour_viridis_c() +
    guides(colour = guide_legend(position = "inside")) +
    theme(legend.position.inside = c(0.9, 0.8))

#Inside scale using depreciated approach
mtcars %>% 
  ggplot(aes(cyl, mpg, col = hp)) +
  geom_point() +
  scale_colour_viridis_c() +
  theme(legend.position = c(0.9, 0.8))

^{Created on 2025-10-22 with reprex v2.1.1}

Session info

sessionInfo()
#> R version 4.4.1 (2024-06-14 ucrt)
#> Platform: x86_64-w64-mingw32/x64
#> Running under: Windows 11 x64 (build 22631)
#> 
#> Matrix products: default
#> 
#> 
#> locale:
#> [1] LC_COLLATE=English_United States.utf8 
#> [2] LC_CTYPE=English_United States.utf8   
#> [3] LC_MONETARY=English_United States.utf8
#> [4] LC_NUMERIC=C                          
#> [5] LC_TIME=English_United States.utf8    
#> 
#> time zone: America/Los_Angeles
#> tzcode source: internal
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#>  [1] lubridate_1.9.3 forcats_1.0.0   stringr_1.5.1   dplyr_1.1.4    
#>  [5] purrr_1.0.2     readr_2.1.5     tidyr_1.3.1     tibble_3.2.1   
#>  [9] ggplot2_4.0.0   tidyverse_2.0.0
#> 
#> loaded via a namespace (and not attached):
#>  [1] gtable_0.3.6       compiler_4.4.1     reprex_2.1.1       tidyselect_1.2.1  
#>  [5] xml2_1.3.6         scales_1.4.0       yaml_2.3.10        fastmap_1.2.0     
#>  [9] R6_2.5.1           labeling_0.4.3     generics_0.1.3     curl_5.2.3        
#> [13] knitr_1.50         pillar_1.9.0       RColorBrewer_1.1-3 tzdb_0.4.0        
#> [17] rlang_1.1.4        utf8_1.2.4         stringi_1.8.4      xfun_0.53         
#> [21] fs_1.6.4           S7_0.2.0           viridisLite_0.4.2  timechange_0.3.0  
#> [25] cli_3.6.3          withr_3.0.1        magrittr_2.0.3     digest_0.6.37     
#> [29] grid_4.4.1         rstudioapi_0.16.0  hms_1.1.3          lifecycle_1.0.4   
#> [33] vctrs_0.6.5        evaluate_1.0.0     glue_1.7.0         farver_2.1.2      
#> [37] fansi_1.0.6        rmarkdown_2.28     tools_4.4.1        pkgconfig_2.0.3   
#> [41] htmltools_0.5.8.1

[Breeze-Hu]

Should use guide_colorbar() instead of guide_legend().
I'm not sure if this is the result you want:

library(tidyverse)

mtcars %>% 
  ggplot(aes(cyl, mpg, col = hp)) +
  geom_point() +
  scale_colour_viridis_c() +
  guides(colour = guide_colorbar(position = "inside")) + # here
  theme(legend.position.inside = c(0.9, 0.8))

^{Created on 2025-10-23 with reprex v2.1.1}

[teunbrand]

Breeze-Hu is correct about guide_colourbar(). Another alternative is to use the theme like so:

  theme(
    legend.position = "inside",
    legend.position.inside = c(0.9, 0.8)
  )