Fix legend border artifact in ppc_freqpoly

[utkarshpawade]

Fixes #134

• ppc_freqpoly() and ppc_freqpoly_grouped() displayed a visible dark border around the y legend key due to the color aesthetic from geom_area() bleeding into the legend glyph
• Added guides(fill = guide_legend(override.aes = list(color = NA))) to suppress the outline color in legend keys

Before

After

[Copilot]

Pull request overview

This PR fixes a ggplot2 legend rendering artifact in the posterior predictive check frequency polygon plots (ppc_freqpoly() and, transitively, ppc_freqpoly_grouped()), where the geom_area() outline color was bleeding into the legend key.

Changes:

• Add a guides(fill = guide_legend(override.aes = list(color = NA))) override to suppress the outline color in the fill legend key for ppc_freqpoly().
• Document the fix in NEWS.md.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
R/ppc-distributions.R	Overrides legend aesthetics for the fill guide to remove the unwanted border artifact in freqpoly PPC plots (also affects grouped variant via delegation).
NEWS.md	Adds a changelog entry describing the legend border artifact fix.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.18%. Comparing base (9d6a95b) to head (c259afa).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #537   +/-   ##
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  Coverage   99.18%   99.18%           
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  Files          35       35           
  Lines        6118     6119    +1     
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+ Hits         6068     6069    +1     
  Misses         50       50           

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[jgabry]

Thanks! I made one review comment. Also, do we have the same issue with ppd_freqpoly or just the ppc_ version?

[utkarshpawade]

No, ppd_freqpoly doesn't have the issue, it calls legend_none() (ppd-distributions.R:283) since there's no y vs yrep distinction to show. The legend-border artifact is specific to ppc_freqpoly/ppc_freqpoly_grouped.

[jgabry]

Thinking about this a bit more, maybe we actually want the border in the plot? For example, with low alpha levels y and yrep can look similar except for the outline. This PR would remove the outline. What do you think?

[utkarshpawade]

I checked this and guide_legend(override.aes = list(color = NA)) only affects the legend key glyph, not the plot geoms. The geom_area() outlines in the plot are untouched, so the low-alpha distinguishability between y and yrep you mentioned is preserved.
Comparison at alpha = 0.3:

Before:

legend key has a dark border box around the y glyph:

After:

legend key is clean; plot polygons still have their outlines.

[jgabry]

Ok thanks. However, now I'm also wondering why we would actually want to remove the border in the legend. The border is there because the plot also has a border. So isn't the legend more accurate if it includes the border?

[utkarshpawade]

yes, you're right Closing this PR as working-as-intended.

[jgabry]

Ok thanks. Also see here if you haven't seen it yet: #545