LASSO Logistic Regression Analysis

When to Read External Files

Situation	File to Read	Purpose
Need algorithm details	references/algorithm.md	LASSO objective function, cross-validation, and interpretation
Need to run analysis	scripts/main.R	Execute: Rscript scripts/main.R --input_file ... --group_file ...
Encounter errors	references/troubleshooting.md	Common errors and solutions
Need CLI examples	references/cli-guide.md	Detailed CLI usage examples
Need test data	tests/data/	Sample input files for testing
Need workflow implementation details	scripts/run_analysis.R	Inspect orchestration, outputs, and file-writing behavior
Need input-validation or error-handling details	scripts/utils.R, scripts/io.R	Inspect validation, parsing, logging, and standardized safeguards

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Usage

Rscript scripts/main.R \
  --input_file ./expression_matrix.csv \
  --group_file ./groups.csv \
  --case_group case \
  --control_group control \
  --output_dir ./output/ \
  --nfolds 10 \
  --timeout_seconds 1800 \
  --seed 42

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Arguments

Short	Long	Type	Default	Description
-i	--input_file	character	required	Expression matrix file (features as rows, samples as columns)
-g	--group_file	character	required	Group file with sample and group columns
-c	--case_group	character	required	Case class label encoded as 1
-t	--control_group	character	required	Control class label encoded as 0
-f	--feature	character	NULL	Optional feature list file or comma-separated feature names
-n	--nfolds	integer	10	Cross-validation folds: 3, 5, 7, 10
	--cv_title	character	""	Optional title for the cross-validation plot
	--path_title	character	""	Optional title for the coefficient path plot
	--timeout_seconds	integer	1800	Maximum elapsed runtime in seconds
-o	--output_dir	character	./output/	Output directory
-s	--seed	integer	42	Random seed for reproducibility

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Input Format

Expression Matrix (input_file)

Features as rows, samples as columns, CSV or TSV format with feature IDs in the first column.

,Sample01,Sample02,Sample03
TSPAN6,1.8479,1.8318,3.8276
TNMD,0.0349,0.0533,1.3889

Group File (group_file)

CSV or TSV with sample IDs and binary-group labels.

sample,group
Sample01,case
Sample02,control
Sample03,case

Optional Feature File (feature)

One feature per line, or pass a comma-separated feature list directly on the CLI.

TNMD
DPM1
SCYL3

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Output Files

File	Description
coefficient.csv	All coefficients at lambda.min
feature_matrix.csv	Sample-level matrix with original group labels and binary event column
selected_features.txt	Non-zero features at lambda.min excluding the intercept, when available
missing_features.txt	Requested features not found in the matrix, when applicable
lasso_lambda_binary_plot.pdf	Cross-validation curve
lasso_var_binary_plot.pdf	Coefficient path plot
session_info.txt	R session and package version info

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Workflow

Step 1: Validate Input

WHEN checking validation rules or parsing behavior, READ: scripts/utils.R and scripts/io.R

• Check file existence
• Read expression matrix and group file
• Verify samples match between files
• Ensure both classes are present with at least 2 samples per class

Step 2: Prepare Modeling Matrix

WHEN checking class encoding or feature filtering behavior, READ: scripts/modeling.R

• Encode case_group as 1 and control_group as 0
• Optionally restrict to a user-supplied feature panel
• Transpose expression data to sample-by-feature format

Step 3: Fit LASSO Logistic Regression

WHEN understanding the statistical method or lambda selection, READ: references/algorithm.md

• Train a binomial glmnet model with alpha = 1
• Run cv.glmnet to select the optimal lambda
• Extract coefficients at lambda.min

Step 4: Save Results and Visualizations

WHEN checking output generation or plot behavior, READ: scripts/run_analysis.R and scripts/plotting.R

• Save flat output files directly into output_dir
• Generate cross-validation and coefficient path PDF plots
• Leave plot titles empty by default unless the user provides custom titles

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Methods

LASSO Logistic Regression

The model minimizes binomial deviance with an L1 penalty, shrinking weak coefficients to zero and performing embedded feature selection.

Cross-Validation

cv.glmnet evaluates candidate lambda values across nfolds folds and reports lambda.min and lambda.1se.

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Examples

Basic Usage

Rscript scripts/main.R \
  -i ./expression_matrix.csv \
  -g ./groups.csv \
  -c case \
  -t control \
  -o ./output

Use a Feature Panel

Rscript scripts/main.R \
  -i ./expression_matrix.csv \
  -g ./groups.csv \
  -c case \
  -t control \
  -f ./genes.txt \
  -o ./output

Custom Folds and Seed

Rscript scripts/main.R \
  -i ./expression_matrix.csv \
  -g ./groups.csv \
  -c case \
  -t control \
  -n 5 \
  --timeout_seconds 900 \
  -s 123 \
  -o ./output

Custom Plot Titles

Rscript scripts/main.R \
  -i ./expression_matrix.csv \
  -g ./groups.csv \
  -c case \
  -t control \
  --cv_title "LASSO Cross-Validation" \
  --path_title "LASSO Coefficient Paths" \
  --timeout_seconds 1200 \
  -o ./output

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Error Handling

Common Errors

Error	Cause	Solution
SKILL_FILE_NOT_FOUND	Input file does not exist	Check file path
SKILL_EMPTY_FILE	An input file exists but contains no data	Verify the file is not empty
SKILL_PARSE_ERROR	The input file cannot be parsed as CSV or TSV	Check delimiters, headers, and encoding
SKILL_FILE_WRITE_ERROR	The output directory cannot be created or written	Check output path and permissions
SKILL_EMPTY_DATA	The loaded table has no usable rows or columns	Verify that the input file contains valid data
SKILL_MISSING_COLUMNS	The group file does not provide the required columns	Provide sample and group columns
SKILL_INVALID_TYPE	A parameter or data field has the wrong type	Ensure numeric fields are numeric and strings are valid
SKILL_SAMPLE_MISMATCH	Sample IDs differ between matrix and group file	Make names match exactly
SKILL_INVALID_GROUP	Case/control labels not found in group file	Check --case_group and --control_group
SKILL_INVALID_DATA	Too few classes, samples, or valid features	Review input structure and feature list
SKILL_INVALID_PARAMETER	Unsupported nfolds or empty parameter	Use documented argument values
SKILL_DEPENDENCY_MISSING	Required R package not installed	Install missing CRAN package
SKILL_TIMEOUT	Analysis exceeded the configured time limit	Reduce feature count or increase --timeout_seconds
SKILL_MEMORY_ERROR	The runtime environment cannot allocate enough memory	Reduce matrix size or available workload
SKILL_RUNTIME_ERROR	An unexpected runtime error occurred	Review the exact console error and retry

IF error persists, READ: references/troubleshooting.md

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Testing

Test with Sample Data

# Check help
Rscript scripts/main.R --help

# Run with sample data
Rscript scripts/main.R \
  -i tests/data/expression_matrix.csv \
  -g tests/data/groups.csv \
  -c case \
  -t control \
  -f tests/data/genes.csv \
  --timeout_seconds 1800 \
  -o tests/output

Validation Commands

# Check coefficient output
ls -la tests/output/coefficient.csv

# Check plots exist
ls -la tests/output/lasso_lambda_binary_plot.pdf
ls -la tests/output/lasso_var_binary_plot.pdf

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Implementation Checklist

• CLI parsing with optparse
• set.seed() for reproducibility
• requireNamespace() dependency checks
• Session info recording
• Timeout control with --timeout_seconds
• Temp file cleanup
• File reading instructions in SKILL.md
• Modular script structure (<150 lines per file)
• Test data provided
• Error handling with SKILL_* codes
• Scripts in scripts/ directory
• References in references/ directory

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Last updated: 2026-04-17 | Version: 1.0.0