Ggplot2 Customization For Statistical Plots

---
name: ggplot2-customization-for-statistical-plots
description: Use when when a statistical analysis function (e.g., random_forest or
  PCA_plot from Omu) returns a ggplot2 object and you need to adjust visual presentation—such
  as removing gridlines, applying a clean background theme (e.
license: CC-BY-4.0
metadata:
  edam_operation: http://edamontology.org/operation_0337
  edam_topics:
  - http://edamontology.org/topic_0091
  - http://edamontology.org/topic_3678
  tools:
  - R
  - ggplot2
  - Omu (plot_variable_importance, PCA_plot, plot_bar)
  license_tier: open
  provenance_tier: literature
derived_from:
- doi: 10.1128/mra.00129-19
  title: omu metabolomics count data tool
evidence_spans:
- Omu is an R package that enables rapid analysis of Metabolomics data sets
- The figure is a ggplot2 object, so it is compatible with any ggplot2 themes
- The figure is a ggplot2 object, so it is compatible with any ggplot2 themes you
  wish to use to edit the appearance
claims: []
provenance:
  collection: https://w3id.org/holobiomicslab/asb-skill/collection/metabolomics/v2
  assembled_by: scripts/collect_metabolomics_collection.py
  sources:
  - build: coll_omu_metabolomics_count_data_tool_cq
    doi: 10.1128/mra.00129-19
    title: omu metabolomics count data tool
  dedup_kept_from: coll_omu_metabolomics_count_data_tool_cq
schema_version: 0.2.0
attribution:
  generator: AgenticScienceBuilder
  original_doi: 10.1128/mra.00129-19
  all_source_dois:
  - 10.1128/mra.00129-19
  zenodo_doi: 10.5281/zenodo.20794027
  curators: []
  promoter: Louis-Félix Nothias
  sponsor: CNRS & Université Côte d'Azur
---

# ggplot2-customization-for-statistical-plots

## Summary

Customize ggplot2 statistical visualizations (e.g., variable importance plots from random forest models) by layering ggplot2 themes and removing default visual elements to produce publication-ready figures. This skill is essential when wrapper functions return ggplot2 objects that require aesthetic refinement without altering the underlying data or statistical computation.

## When to use

When a statistical analysis function (e.g., random_forest or PCA_plot from Omu) returns a ggplot2 object and you need to adjust visual presentation—such as removing gridlines, applying a clean background theme (e.g., theme_bw), or aligning the figure with journal or presentation standards—without re-computing the statistical result.

## When NOT to use

- Input is a base R plot (not a ggplot2 object); use base R par() or plot() parameters instead.
- You need to modify the underlying statistical computation or data; use filter_steps or workflow steps to transform inputs before passing to the visualization function.
- The visualization function does not return a ggplot2 object; consult the function documentation or apply tool-specific customization methods.

## Inputs

- ggplot2 object (e.g., from plot_variable_importance, PCA_plot, or plot_bar functions)
- Optionally: ggplot2 theme name or custom theme definition

## Outputs

- Customized ggplot2 object suitable for publication or presentation
- Rendered figure (PNG, PDF, or display)

## How to apply

After obtaining a ggplot2 object from a statistical wrapper (e.g., plot_variable_importance output), apply ggplot2 theme functions to modify the plot's appearance. Use theme_bw() or other ggplot2 built-in themes to standardize the background and axis styling. Remove unwanted visual elements—such as major or minor gridlines—using theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank()). Stack these modifications as additional layers using the + operator, which does not alter the statistical content or data representation, only the rendering. Test the final figure visually to ensure clarity and alignment with publication or presentation goals.

## Related tools

- **ggplot2** (Core graphics library providing theme functions, element_blank(), and the + operator for layering aesthetic customizations onto statistical plot objects)
- **Omu (plot_variable_importance, PCA_plot, plot_bar)** (Wrapper functions that return ggplot2 objects as input to this customization skill) — https://github.com/connor-reid-tiffany/Omu

## Examples

```
# After obtaining a random forest plot from Omu:
rf_plot <- plot_variable_importance(rf_model)
customized_plot <- rf_plot + theme_bw() + theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank())
print(customized_plot)
```

## Evaluation signals

- The returned object is still a valid ggplot2 object (class 'gg' and 'ggplot'); verify using class(plot_object).
- Visual inspection confirms that gridlines are removed or themes are applied as intended without altering axis labels, legends, or statistical annotations.
- The customized plot renders without errors and can be saved to disk using ggsave() or exported to publication formats (PNG, PDF).
- Statistical content (e.g., variable importance rankings, PC loadings, bar heights) remains identical to the pre-customization version; only visual styling has changed.
- The plot meets journal or presentation style guidelines (e.g., black-and-white theme, no gridlines, readable font sizes).

## Limitations

- ggplot2 customization does not alter the underlying statistical computation; if the statistical result is incorrect, theme modifications alone cannot fix it.
- Theme and element functions are specific to ggplot2 syntax; base R plots or plots from other libraries (e.g., plotly, lattice) require different customization approaches.
- Over-customization (e.g., removing all gridlines and axis labels) may reduce clarity; balance aesthetics with readability.
- The article does not document specific theme recommendations or best practices for different metabolomics visualization types beyond the example of theme_bw() and gridline removal.

## Evidence

- [other] The figure is a ggplot2 object, so it is compatible with any ggplot2 themes: "The figure is a ggplot2 object, so it is compatible with any ggplot2 themes"
- [other] customize with ggplot2 themes as desired (e.g., theme_bw, remove gridlines): "customize with ggplot2 themes as desired (e.g., theme_bw, remove gridlines)"