ggplot2: boxplot with facet_grid and free scale

Question

I am trying to have free scales on a Boxplot image with faceting.

Using this example dataset, if I try this:

ggplot(data=mpg) +
geom_boxplot(aes(x=cty, y=model))+
facet_grid(manufacturer ~ drv, scales = "free", space = "free")

Plot incorrect boxplot http://dl.dropbox.com/u/9788680/plot1.png

Here, the free scales are implemented exactly as I would like, with the different scales for the y-axis depending on the number of available factors for a horizontal facet rule. The boxplots are however not correctly depicted (i.e. as solid lines instead of boxplots). When searching for a solution, I found that I should use coord_flip() in order to make the boxplot be depicted correctly, i.e.

ggplot(data=mpg) +
geom_boxplot(aes(x=model,y=cty))+
facet_grid(manufacturer ~ drv, scales = "free", space = "free")+
coord_flip()

Plot correct boxplot, but no scaling http://dl.dropbox.com/u/9788680/plot2.png

In above picture, the boxplots are now correct. However, the free scale for the factors (so on the y-axis) are removed. Now, for each horizontal facet line, ALL the available factors across the dataset are now included, instead of only the factors available for each facet (as in Figure 1).

I would like to know how I can get the correct facetting with a free scale on both axes, correctly depicting the boxplot.

If somebody could point me in the right direction, I would be grateful.

Thanks.

I noticed the same problem when answering http://stackoverflow.com/a/10729264/1385941. My guess is it because coord_flip() calls coord_cartesian not scale_continuous. scale_ and coord_ affect the plot differently. It might be worth reporting this as an issue at https://github.com/hadley/ggplot2 — mnel
Thank you for this comment. Hopefully somebody can provide a workaround. If no other comments are posted I will report this issue as suggested. Maybe an analog to geom_errorbarh could be written for boxplots as well. — coenvh
There is no current workaround; boxplots are only vertical (continuous variable is y) and can only be flipped with coord_flip(), but that messes up the faceting scales, like you see. See groups.google.com/d/msg/ggplot2/u5a1mpnJR7E/XxwXWNDX77MJ — Brian Diggs

Dylan Dylan · Accepted Answer · 2017-07-08T12:34:15

The desired behavior is supported at least as of ggplot2 2.2.1.

library(ggplot2)
ggplot(data=mpg[which(mpg$manufacturer %in% c('audi', 'hyundai', 'jeep')),]) +
  geom_boxplot(aes(x=model,y=cty)) +
  facet_grid(manufacturer ~ drv, scales = "free", space = "free") +
  coord_flip()

sessionInfo()
#> R version 3.3.2 (2016-10-31)
#> Platform: x86_64-apple-darwin13.4.0 (64-bit)
#> Running under: OS X El Capitan 10.11.6
#> 
#> locale:
#> [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] ggplot2_2.2.1
#> 
#> loaded via a namespace (and not attached):
#>  [1] Rcpp_0.12.11         digest_0.6.12        rprojroot_1.2       
#>  [4] plyr_1.8.4           grid_3.3.2           gtable_0.2.0        
#>  [7] backports_1.0.5      magrittr_1.5         evaluate_0.10.1     
#> [10] scales_0.4.1.9002    rlang_0.1.1.9000     stringi_1.1.5       
#> [13] reshape2_1.4.2       lazyeval_0.2.0       rmarkdown_1.6.0.9001
#> [16] labeling_0.3         tools_3.3.2          stringr_1.2.0       
#> [19] munsell_0.4.3        yaml_2.1.14          colorspace_1.3-2    
#> [22] htmltools_0.3.6      knitr_1.16           tibble_1.3.3

ggplot2: boxplot with facet_grid and free scale

2 Answers