How can I programmatically tell how many facets a ggplot has?

Question

Below is code and a graph.

The graph has three facets. Where in the_plot can I find it has three facets? Yes, I could get that from the mtcars data frame, or the_plot$data, but I don't want to recreate the data analysis. Rather, I want to inspect the graphical elements of the_plot, so I don't have to duplicate application logic in multiple places. the_plot$facet doesn't show anything I recognize, nor do the other plot variables.

I'm using tidyverse 1.3.0.

library(tidyverse)
data(mtcars)
the_plot<-ggplot(mtcars, aes(mpg, disp, group=cyl)) + facet_wrap(~cyl) + geom_point()
the_plot

Answer 1

you can access the ggplot data with the gg_build() - function

out <- ggplot_build(the_plot)

length(levels(out$data[[1]]$PANEL))
[1] 3

Answer 2

Another method

library(ggplot2)
data(mtcars)
the_plot<-ggplot(mtcars, aes(mpg, disp, group=cyl)) + facet_wrap(~cyl) + geom_point()
pb <- ggplot_build(the_plot)
pb$layout$layout$PANEL
#> [1] 1 2 3
#> Levels: 1 2 3

^{Created on 2020-04-21 by the reprex package (v0.3.0)}