添加guides='collect'致patchwork报错：Error in as.unit(value) : object is not coercible to a unit

问题重现 #

以下代码原本可正常生成组合图形，但在plot_layout中添加guides = "collect"参数后，触发报错：Error in as.unit(value) : object is not coercible to a unit。

可复现代码 #

library(tidyverse)
library(magrittr)
library(patchwork)

d1 <- tibble(
  x = rep(1, 5),
  y = rep(1, 5),
  col = letters[1:5]
)

p1 <- ggplot(
  aes(x, y, color = col),
  data = d1 %>% slice(1:3)
) +
  facet_wrap(~col, nrow = 1) +
  geom_point(size = 5) 

p2 <- ggplot(
  aes(x, y, color = col),
  data = d1 %>% slice(4:5)
) +
  facet_wrap(~col, nrow = 1) +
  geom_point(size = 5)

# 触发报错的代码
p1 / p2 +
  plot_layout(
    design = "
    111
    22#
    ",
    guides = "collect"
  )

报错信息 #

Error in as.unit(value) : object is not coercible to a unit

环境信息 #

R version 4.4.1 (2024-06-14 ucrt)
Platform: x86_64-w64-mingw32/x64
Running under: Windows 11 x64 (build 26120)

Matrix products: default


locale:
[1] LC_COLLATE=English_United States.utf8  LC_CTYPE=English_United States.utf8   
[3] LC_MONETARY=English_United States.utf8 LC_NUMERIC=C                           
[5] LC_TIME=English_United States.utf8    

time zone: Australia/Sydney
tzcode source: internal

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

other attached packages:
 [1] patchwork_1.2.0      magrittr_2.0.3       lubridate_1.9.3      forcats_1.0.0        stringr_1.5.1.9000  
 [6] dplyr_1.1.4          purrr_1.0.2.9000     readr_2.1.5          tidyr_1.3.1          tibble_3.2.1        
[11] ggplot2_3.5.1.9000   tidyverse_2.0.0.9000

loaded via a namespace (and not attached):
 [1] vctrs_0.6.5       cli_3.6.3         rlang_1.1.4       stringi_1.8.4     generics_0.1.3   
 [6] labeling_0.4.3    glue_1.7.0        colorspace_2.1-1  hms_1.1.3         scales_1.3.0     
[11] fansi_1.0.6       grid_4.4.1        munsell_0.5.1     tzdb_0.4.0        lifecycle_1.0.4  
[16] compiler_4.4.1    timechange_0.3.0  pkgconfig_2.0.3   rstudioapi_0.16.0 farver_2.1.2     
[21] R6_2.5.1          tidyselect_1.2.1  utf8_1.2.4        pillar_1.9.0      tools_4.4.1      
[26] withr_3.0.1       gtable_0.3.5     

解决方案 #

这个报错源于patchwork在收集分面图的图例时，与自定义布局中的占位符#存在兼容性冲突。可以通过以下两种方式解决：

方案1：移除布局占位符，使用默认布局收集图例 #

如果不需要保留占位符的空白区域，直接移除design参数或调整为无占位符的设计即可：

p1 / p2 + plot_layout(guides = "collect")

方案2：手动分离图例，自定义布局放置 #

先移除子图的图例，单独创建图例区域，再通过design参数指定布局位置：

# 移除子图的图例
p1_no_guide <- p1 + theme(legend.position = "none")
p2_no_guide <- p2 + theme(legend.position = "none")

# 组合子图与图例区域
combined <- p1_no_guide / p2_no_guide + guide_area()

# 指定布局，用3代表图例区域
combined + plot_layout(design = "
    111
    223
    ")

内容的提问来源于stack exchange，提问作者tomw