sample-group-sankey-plot

name	sample-group-sankey-plot
description	Use when generating Sankey or alluvial plots from sample annotation tables where rows are samples and selected columns are categorical stages such as risk group, response status, subtype, or cohort labels. NOT for: gene network flow analysis, continuous-value trajectories, or graph-structured pathway visualization.
license	MIT
skill-author	AIPOCH

Sample Group Sankey Plot

Builds a reproducible Sankey/alluvial visualization from a tabular sample annotation file and exports the selected annotations, lodes-format table, plot PDF, and session metadata.

Input Validation

This skill accepts: a sample annotation table in CSV or TSV format where rows are samples and selected columns are categorical stages (e.g., risk group, response status, subtype, cohort label). At least 2 stage columns are required.

If the user's request does not involve generating a Sankey or alluvial flow diagram from categorical sample annotations — for example, asking to visualize a gene regulatory network, plot continuous-value trajectories, analyze pathway flow, or process non-tabular data — do not proceed with the workflow. Instead respond:

"sample-group-sankey-plot is designed to generate Sankey/alluvial plots from categorical sample annotation tables. Your request appears to be outside this scope. Please provide a sample annotation table with at least 2 categorical stage columns, or use a more appropriate tool for gene network visualization or pathway analysis."

Readability guidance: Sankey plots are recommended for fewer than 8 unique values per stage and fewer than 5 stages total. For larger inputs, filter or aggregate categories before plotting to ensure readable output.

Agent Response Contract

After a successful run, report to the caller:

Sankey plot generated successfully.
Stages plotted : <comma-separated stage column names>
Samples        : <row count>
Output prefix  : <output_prefix>
Outputs:
  table/selected_annotations.csv
  table/sankey_lodes.csv
  plot/<output_prefix>.pdf
  data/session_info.txt
Readability warnings (if any): <advisory messages or "none">

If the script exits with a non-zero status, surface the SKILL_* error code and message verbatim. Do not attempt to continue or retry silently.

When to Read External Files

Situation	File to Read	Purpose
Need to run analysis	scripts/main.R	Execute: Rscript scripts/main.R --input_file ... --output_dir ...
Need algorithm details	references/algorithm.md	Alluvial transformation logic, assumptions, and plotting choices
Encounter errors	references/troubleshooting.md	Common errors and solutions
Need CLI examples	references/cli-guide.md	Detailed CLI examples
Need test data	tests/data/	Sample annotation tables for smoke tests and regression checks

→ Reference files algorithm.md, troubleshooting.md, and cli-guide.md are in references/. If absent, rely on the Error Handling table below for common issues.

---

Usage

Environment Setup

Install required R packages before the first run:

Rscript scripts/install_dependencies.R

Note: install_dependencies.R installs from CRAN without version pinning. Tested with ggalluvial >= 0.12.5 and ggplot2 >= 3.4.0. For reproducible CI environments, consider using remotes::install_version().

Basic Command

Rscript scripts/main.R \
  --input_file ./annotations.csv \
  --output_dir ./output \
  --columns risk,Responder \
  --seed 42

---

Arguments

Short	Long	Type	Default	Description
-i	--input_file	character	required	Input CSV/TSV annotation table
-o	--output_dir	character	./output/	Output directory
-c	--columns	character	all columns	Comma-separated stage columns to include in the plot. When omitted, all columns in the file are used as stages.
-p	--output_prefix	character	sankey_plot	Prefix for generated output files (alphanumeric, dot, underscore, or hyphen characters only)
	--width	numeric	7	Plot width in inches
	--height	numeric	5	Plot height in inches
	--alpha	numeric	0.5	Flow transparency between 0 and 1
	--label_size	numeric	4.5	Stratum label size
	--missing_label	character	Missing	Replacement label for blank or NA strata
	--title	character	empty	Optional plot title
-s	--seed	integer	42	Random seed recorded for reproducibility
	--timeout	integer	3600	Maximum allowed elapsed runtime in seconds; use to disable

---

Input Format

Annotation Table (input_file)

Delimited text file where rows represent samples and each selected column is a categorical stage shown in the Sankey plot.

SampleID,risk,Responder,Subtype
S1,High,Yes,Basal
S2,Low,No,LumA
S3,High,Yes,Basal
S4,Low,No,LumB

Requirements:

• The file must contain at least 2 columns if --columns is omitted.
• Each selected column must exist in the file header.
• Selected columns are interpreted as categorical stages and will be converted to character values.
• Blank strings and NA values are replaced with --missing_label.
• CSV and TSV inputs are supported.
• Recommended: fewer than 8 unique values per stage and fewer than 5 stages total for readable plots.

---

Output Files

File	Description
table/selected_annotations.csv	Filtered table containing only the plotted stage columns
table/sankey_lodes.csv	Long-format lodes table used to build the Sankey plot
plot/{output_prefix}.pdf	Sankey/alluvial plot as a PDF file; default filename is sankey_plot.pdf
data/session_info.txt	R session information and runtime parameters

selected_annotations.csv

Column	Type	Description
stage columns	character	One column per plotted stage in original order

sankey_lodes.csv

Column	Type	Description
sample_id	character	Synthetic row identifier used as the alluvium key
x	character	Stage name
stratum	character	Category label for the stage

---

Workflow

Step 1: Validate Input

• Check that the input file exists and is readable.
• Detect CSV vs TSV input.
• Validate that at least 2 stage columns are available.
• Validate that user-specified columns exist.

Step 2: Prepare Sankey Data

• Subset the selected stage columns.
• Replace missing or blank labels.
• Add a row-level sample_id identifier.
• Convert the table with ggalluvial::to_lodes_form().

Step 2a: Readability Advisories

After column selection, the script emits log_warn advisories when:

• More than 5 stages are selected: "More than 5 stages selected; plot may be hard to read. Consider filtering."
• A stage has more than 8 unique values: "Stage <name> has <n> unique values; consider aggregating for readability."

These are advisory only — the script continues and produces the plot.

Step 3: Generate Visualization

• Build the Sankey/alluvial plot with geom_flow() and geom_stratum().
• Render stratum labels.
• Save the plot as PDF.

Step 4: Record Outputs

• Save the selected annotations and lodes-format table as CSV files.
• Save sessionInfo() and runtime arguments for reproducibility.

---

Examples

Reproduce the Original Two-Column Plot

Rscript scripts/main.R \
  -i tests/data/sample_annotations.csv \
  -o tests/output \
  -c risk,Responder

Plot Three Annotation Stages

Rscript scripts/main.R \
  -i tests/data/sample_annotations.csv \
  -o tests/output_three_stage \
  -c risk,Responder,Subtype \
  --title "Risk to response transitions"

Use All Columns Automatically

Rscript scripts/main.R \
  -i tests/data/minimal_annotations.csv \
  -o tests/output_all_columns

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Error Handling

Common Errors

Error	Cause	Solution
SKILL_FILE_NOT_FOUND	Input file does not exist	Check --input_file
SKILL_EMPTY_DATA	The input file has zero rows or fewer than 2 usable columns	Provide a non-empty table with at least 2 stage columns
SKILL_MISSING_COLUMNS	A requested stage column is absent	Correct --columns or fix the input header
SKILL_INVALID_PARAMETER	Width, height, alpha, label size, or output prefix is invalid	Provide valid arguments per the Arguments table
SKILL_DEPENDENCY_MISSING	A required R package is unavailable	Run Rscript scripts/install_dependencies.R
SKILL_IO_ERROR	Output directory cannot be created or written	Check permissions on --output_dir

IF error persists, READ: references/troubleshooting.md

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Testing

Test with Sample Data

Rscript scripts/install_dependencies.R

Rscript scripts/main.R --help

Rscript scripts/main.R \
  -i tests/data/sample_annotations.csv \
  -o tests/output \
  -c risk,Responder,Subtype

Rscript tests/test_skill.R

Rscript tests/run_smoke_test.R

Validation Commands

ls -la tests/output/table
ls -la tests/output/plot
ls -la tests/output/data

---

References

1. Brunson JC (2020) ggalluvial: Layered Grammar for Alluvial Plots. Journal of Open Source Software. doi:10.21105/joss.02017
2. Wickham H (2016) ggplot2: Elegant Graphics for Data Analysis. Springer. doi:10.1007/978-3-319-24277-4

For detailed algorithm, READ: references/algorithm.md