Internal Design of `kvr2`

Overview

The kvr2 package is designed not only to calculate statistics but also to serve as an educational tool for understanding the behavior of \(R^2\) definitions under various model specifications (e.g., with vs. without intercept).

To balance compatibility with external table-formatting packages (like insight) and high-performance visualization (using ggplot2 and grid), the package adopts a “Metadata-Rich Data Frame” architecture.

Data Flow Architecture

The internal process follows a three-stage pipeline:

1. Extraction Phase (`values_lm`)

The core extraction function values_lm() deconstructs an lm object into its mathematical essentials:

\(SS_{res}\) (Residual Sum of Squares)
\(SS_{tot}\) (Total Sum of Squares)
\(n\) (Sample size) and \(k\) (Number of parameters)
Identity of the response and predictor variables.

This decoupling ensures that the downstream calculation functions remain lightweight and do not depend directly on the complex lm object structure.

2. Computation and Metadata Injection (`r2`, `comp_model`)

In this phase, the package calculates the nine \(R^2\) definitions. Crucially, it embeds the model’s context as S3 Attributes.

r2_kvr2 objects: Store metadata such as type (“linear” or “power”), n, k, and has_intercept.
comp_model objects: Inherit data.frame properties for easy printing, while storing the original lm objects as hidden attributes (with_int and without_int).

3. Dispatch and Visualization Phase

The S3 methods (print, plot, model_info) leverage these hidden attributes:

model_info(): Acts as a “metadata extractor,” providing transparency into how degrees of freedom were handled.
plot.comp_model(): Recovers the original lm objects from attributes to generate diagnostic plots on the fly, without requiring the user to pass the models again.

Handling Non-Standard Evaluation (NSE)

To ensure the package passes R CMD check without “no visible binding for global variable” notes, all ggplot2 calls use the .data pronoun from the rlang package.

# Example of internal safety
ggplot2::aes(x = .data$Definition, y = .data$Value)

Dependency Strategy

The package follows a “Low-Maintenance Dependency” philosophy:

**ggplot2 & tidyr**: Core dependencies for modern visualization and data reshaping.
grid: A base R package used for multi-panel layouts (2x2 dashboards) to avoid the overhead of additional layout packages like patchwork or cowplot.
insight: Used for professional console output formatting.

Troubleshooting and Maintenance

When debugging, developers should inspect the object’s “hidden life” using the following commands:

Command	Purpose
`attributes(obj)`	Check if metadata (n, k, model objects) is preserved.
`model_info(obj)`	Verify the mathematical assumptions used for calculation.
`unclass(obj)`	View the underlying list structure without S3 method interference.

Internal Design

Internal Design of kvr2