Ari Lamstein

Update: “Difficult to Reproduce Choroplethr Bug” Isolated and Fixed

Yesterday I wrote that I’ve received a number of choroplethr bug reports recently that I simply cannot reproduce. Due to a large number of people replying with their system information, along with whether or not they were able to reproduce the bug, I was able to track it down. Thank you to everyone who helped!

It appears that the issue only occurs when choroplethr is used in conjunction with the development version of ggplot2. I personally never use the development version of ggplot2, which explains why I was never able to reproduce the bug.

Normally I would not update choroplethr to work better with the development version of another package. But I received a lot of help to isolate this issue, so I decided to submit a fix to github. You can get it by typing the following:

# install the "ggplot2-dev-fix" branch of choroplethr

# verify that this version works with your version of ggplot2


If you were able to reproduce the bug before, I would appreciate it if you could retest with this version and verify that everything now works for you.

Technical Details

In order to create a map of the 50 US States, choroplethr first renders a map of the continental United States. It then individually renders Alaska and Hawaii, and affixes them to the continental US map as annotations. You can view the entire process here. A key function in that process is this line:

alaska.grob = ggplotGrob(alaska.ggplot)

With the development version of ggplot2, the call to ggplotGrob fails. It appears that the failure is due to changes in how the development version of ggplot2 handles themes. Choroplethr uses two custom themes:

  • theme_clean hides hides everything except the map and legend.
  • theme_inset acts like theme_clean but also hides the legend.

You can view the choroplethr theme code here.

I’m not an expert on these new changes to ggplot2, but it appears that ggplotGrob now wants a theme with all member variables specified. It also appears that there is a new built-in theme called theme_void that does everything my theme_clean does while also setting all of the theme member variables. (This means that calling ggplotGrob with theme_void does not lead to a crash). I used theme_void as the basis of my fix. You can see the specific code change here.

(As a note to myself, it now appears that using one of the theme_replace functions would simplify the code of my new theme_inset code. I am intentionally holding off on this change, though, until I know whether or not this will even be an issue in the next CRAN version of ggplot2).

Ari Lamstein

Ari Lamstein

I currently work as a Staff Data Science Engineer at a marketing analytics consultancy. I have 20 years experience developing software in areas such as data science, web development and video games. I have also worked as a technical trainer and independent consultant.

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