pywombat 0.2.0

A CLI tool for processing and filtering bcftools tabulated TSV files with pedigree support

PyWombat

A CLI tool for processing bcftools tabulated TSV files.

Installation

This is a UV-managed Python package. To install:

uv sync

Usage

The wombat command processes bcftools tabulated TSV files:

# Format a bcftools TSV file and print to stdout
wombat input.tsv

# Format and save to output file (creates output.tsv by default)
wombat input.tsv -o output

# Format and save as parquet
wombat input.tsv -o output -f parquet
wombat input.tsv -o output --format parquet

# Format with pedigree information to add parent genotypes
wombat input.tsv --pedigree pedigree.tsv -o output

What does wombat do?

The wombat command processes bcftools tabulated TSV files by:

1. Expanding the (null) column: This column contains multiple fields in the format NAME=value separated by semicolons (e.g., DP=30;AF=0.5;AC=2). Each field is extracted into its own column.

2. Preserving the CSQ column: The CSQ (Consequence) column is preserved as-is and not melted, allowing VEP annotations to remain intact.

3. Melting and splitting sample columns: After the (null) column, there are typically sample columns with values in GT:DP:GQ:AD format. The tool:

   • Extracts the sample name (the part before the first : character)
   • Transforms the wide format into long format
   • Creates a sample column with the sample names
   • Splits the sample values into separate columns:
     • sample_gt: Genotype (e.g., 0/1, 1/1)
     • sample_dp: Read depth
     • sample_gq: Genotype quality
     • sample_ad: Allele depth (takes the second value from comma-separated list)
     • sample_vaf: Variant allele frequency (calculated as sample_ad / sample_dp)

Example

Input:

CHROM POS REF ALT (null) Sample1:GT:Sample1:DP:Sample1:GQ:Sample1:AD Sample2:GT:Sample2:DP:Sample2:GQ:Sample2:AD
chr1 100 A T DP=30;AF=0.5;AC=2 0/1:15:99:5,10 1/1:18:99:0,18

Output:

CHROM POS REF ALT AC AF DP sample sample_gt sample_dp sample_gq sample_ad sample_vaf
chr1 100 A T 2 0.5 30 Sample1 0/1 15 99 10 0.6667
chr1 100 A T 2 0.5 30 Sample2 1/1 18 99 18 1.0

Notes:

• The sample_ad column contains the second value from the AD field (e.g., from 5,10 it extracts 10)
• The sample_vaf column is the variant allele frequency calculated as sample_ad / sample_dp
• By default, output is in TSV format. Use -f parquet to output as Parquet files
• The -o option specifies an output prefix (e.g., -o output creates output.tsv or output.parquet)

Pedigree Support

You can provide a pedigree file with the --pedigree option to add parent genotype information to the output. This enables trio analysis by including the father's and mother's genotypes for each sample.

Pedigree File Format:

The pedigree file should be a tab-separated file with the following columns:

• FID: Family ID
• sample_id: Sample identifier (matches the sample names in the VCF)
• FatherBarcode: Father's sample identifier (use 0 or -9 if unknown)
• MotherBarcode: Mother's sample identifier (use 0 or -9 if unknown)
• Sex: Sex of the sample (optional)
• Pheno: Phenotype information (optional)

Example pedigree file:

FID sample_id FatherBarcode MotherBarcode Sex Pheno
FAM1 Child1 Father1 Mother1 1 2
FAM1 Father1 0 0 1 1
FAM1 Mother1 0 0 2 1

Output with Pedigree:

When using --pedigree, the output will include additional columns for each parent:

• father_gt, father_dp, father_gq, father_ad, father_vaf: Father's genotype information
• mother_gt, mother_dp, mother_gq, mother_ad, mother_vaf: Mother's genotype information

These columns will contain the parent's genotype data for the same variant, allowing you to analyze inheritance patterns.

Development

This project uses:

• UV for package management
• Polars for fast data processing
• Click for CLI interface

Testing

Test files are available in the tests/ directory:

• test.tabulated.tsv - Real bcftools output
• test_small.tsv - Small example for quick testing