adding ppc_rootogram_grouped function

[behramulukir]

This PR adds ppc_rootogram_grouped function requested at #377. If you have any feedback, I am happy to hear @mhollanders.

ppc_rootogram_grouped simply creates multiple facets (plots) of the rootogram based on the grouping user passes to the function as an argument.

Something to note here is that in ppc_bars_grouped, force_axes_in_facets function is used to make sure all facets have axes. This was resulting in errors when used with ppc_rootogram_grouped(style="discrete") since -Inf results in NaN when used with scale_y_sqrt(). It was still used in other rootogram styles, but so far, I hadn't managed to get it working for discrete style. I'll mark this PR as ready once I find a solution to that.

Tasks:

• implement functions
• implement tests
• update documentation
• fixing axes in discrete style

Examples

y <- rpois(100, 20)
yrep <- matrix(rpois(10000, 20), ncol = 100)
group <- gl(2, 50, length = 100, labels = c("GroupA", "GroupB"))

ppc_rootogram_grouped(y, yrep, group, prob = 0.5)

ppc_rootogram_grouped(y, yrep, group, prob = 0.5, style = "discrete")

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.66%. Comparing base (d831b30) to head (16f1338).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #419      +/-   ##
==========================================
+ Coverage   98.62%   98.66%   +0.04%     
==========================================
  Files          35       35              
  Lines        5798     5830      +32     
==========================================
+ Hits         5718     5752      +34     
+ Misses         80       78       -2     

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[mhollanders]

Fantastic, thank you! I will doubtlessly have a use case for this in the next two weeks, and I will report if there's any issues.

[mhollanders]

@behramulukir, sorry for the basic question, but how do I get to the function? I don't see it when I install the latest development version of bayesplot.

[behramulukir]

Did you install the correct branch @mhollanders? As the changes are not merged to the master branch yet, you should install the branch I am working on. You can do it with devtools::install_github("stan-dev/bayesplot", ref = "ppc-rootogram-grouped")