如何从 ggplot2 scale_color_manual() 中删除未使用的值？

Question

我认为这是 ggplot2 最近的一个变化，scale_manual 函数中定义的所有值都包含在图例中，但我只想要图例中数据集中的值。

下面是一个最小的示例，其中“C”已从数据集中过滤出来，但仍然出现在图例中。有没有简单的修复方法可以从图例中删除“C”？

library(ggplot2)
library(dplyr)

df_dummy <- tribble(
    ~label, ~x, ~y,
    "A",     1,  1,
    "B",     2,  2,
    "C",     3,  3,
    "D",     4,  4
)

myColors <- viridis::viridis_pal(option = "H")(4)
names(myColors) <- factor(df_dummy$label)
dummy_col_scale <- scale_color_manual(name = "Legend", values = myColors)

df_dummy %>% 
    filter(label != "C") %>% 
    ggplot(aes(x, y, color = label)) +
    geom_point() +
    dummy_col_scale

sessionInfo()

R version 4.0.3 (2020-10-10)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19044)

Matrix products: default

locale:
[1] LC_COLLATE=English_Australia.1252 
[2] LC_CTYPE=English_Australia.1252   
[3] LC_MONETARY=English_Australia.1252
[4] LC_NUMERIC=C                      
[5] LC_TIME=English_Australia.1252    

attached base packages:
[1] stats     graphics  grDevices utils    
[5] datasets  methods   base     

other attached packages:
[1] dplyr_1.0.5   ggplot2_3.3.5

loaded via a namespace (and not attached):
 [1] rstudioapi_0.13   magrittr_2.0.1   
 [3] tidyselect_1.1.1  munsell_0.5.0    
 [5] cowplot_1.1.1     viridisLite_0.4.0
 [7] colorspace_2.0-2  R6_2.5.1         
 [9] rlang_0.4.10      fansi_0.4.2      
[11] tools_4.0.3       grid_4.0.3       
[13] gtable_0.3.0      utf8_1.2.1       
[15] cli_3.0.1         DBI_1.1.1        
[17] withr_2.4.2       ellipsis_0.3.2   
[19] digest_0.6.27     assertthat_0.2.1 
[21] tibble_3.1.1      lifecycle_1.0.1  
[23] crayon_1.4.1      gridExtra_2.3    
[25] farver_2.1.0      purrr_0.3.4      
[27] viridis_0.6.0     vctrs_0.3.8      
[29] glue_1.4.2        labeling_0.4.2   
[31] compiler_4.0.3    pillar_1.6.4     
[33] generics_0.1.0    scales_1.1.1     
[35] pkgconfig_2.0.3  

Answer 1

一种选择是设置limits = force在scale_color_manual.

df_dummy <- structure(list(label = c("A", "B", "C", "D"), x = c(1, 2, 3, 
4), y = c(1, 2, 3, 4)), class = c("tbl_df", "tbl", "data.frame"
), row.names = c(NA, -4L))

myColors <- viridis::viridis_pal(option = "H")(4)
names(myColors) <- factor(df_dummy$label)

dummy_col_scale <-
  scale_color_manual(name = "Legend",
                     values = myColors,
                     limits = force)

df_dummy %>%
  filter(label != "C") %>%
  ggplot(aes(x, y, color = label)) +
  geom_point() +
  dummy_col_scale

输出