Cohort 3, chapter 19: (#58)

* Cohort 3, chapter 19:

To aid slidedeck navigation

* separated long slides into separate slides
* folded longer code blocks into details
* hid "TODO" elements

The previous cohort correctly noted that some codes do not work at the moment.  I commented out what wasn't working at the moment and set "eval = TRUE" for the rest of the code.

* Update 19-ggplot2-internals.Rmd

* Clean up + explicitly namespace map.

---------

Co-authored-by: Jon Harmon <[email protected]>

Author: dsollberger

13-build-plot.Rmd

@@ -458,6 +458,9 @@ p4<-ggplot(mpg, aes(cty, hwy)) +
 p3+p4
 ```
 
+```{r include=FALSE}
+rm(class, map) # Clean up so these objects don't confuse later chapters.
+```
 
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