## Extension Function Catalog

This section is generated from `functions.yaml`.

### Readers

| Function | Kind | Returns | R helper | Description |
| --- | --- | --- | --- | --- |
| `read_bcf` | table | table | `rduckhts_bcf` | Read VCF and BCF variant data with typed INFO, FORMAT, typed CSQ/ANN/BCSQ subfields, optional tidy sample output, and optional bcftools-style CSQ type overrides. |
| `read_bam` | table | table | `rduckhts_bam` | Read SAM, BAM, and CRAM alignments with optional typed SAMtags and auxiliary tag maps. Use sequence_encoding := 'nt16' to return SEQ as UTINYINT[] and quality_representation := 'phred' to return QUAL as UTINYINT[] instead of VARCHAR. |
| `read_fasta` | table | table | `rduckhts_fasta` | Read FASTA records or indexed FASTA regions as sequence rows. Use sequence_encoding := 'nt16' to return SEQUENCE as UTINYINT[] (htslib nt16 4-bit codes) instead of VARCHAR. |
| `read_bed` | table | table | `rduckhts_bed` | Read BED3-BED12 interval files with canonical typed columns and optional tabix-backed region filtering. |
| `fasta_nuc` | table | table | `rduckhts_fasta_nuc` | Compute bedtools nuc-style nucleotide composition for supplied BED intervals or generated fixed-width bins over a FASTA reference. |
| `read_fastq` | table | table | `rduckhts_fastq` | Read single-end, paired-end, or interleaved FASTQ files with optional legacy quality decoding. By default, FASTQ qualities are interpreted as modern Phred+33 input. Use sequence_encoding := 'nt16' to return SEQUENCE as UTINYINT[] and quality_representation := 'phred' to return QUALITY as UTINYINT[] instead of VARCHAR. input_quality_encoding accepts 'phred33', 'auto', 'phred64', or 'solexa64'. |
| `read_gff` | table | table | `rduckhts_gff` | Read GFF annotations with optional parsed attribute maps and indexed region filtering. |
| `read_gtf` | table | table | `rduckhts_gtf` | Read GTF annotations with optional parsed attribute maps and indexed region filtering. |
| `read_tabix` | table | table | `rduckhts_tabix` | Read generic tabix-indexed text data with optional header handling and type inference. |
| `fasta_index` | table | table | `rduckhts_fasta_index` | Build a FASTA index (.fai) and return a single row with columns success (BOOLEAN) and index_path (VARCHAR). |

### Metadata

| Function | Kind | Returns | R helper | Description |
| --- | --- | --- | --- | --- |
| `detect_quality_encoding` | table | table | `rduckhts_detect_quality_encoding` | Inspect a FASTQ file's observed quality ASCII range and report compatible legacy encodings with a heuristic guessed encoding. |
| `read_hts_header` | table | table | `rduckhts_hts_header` | Inspect HTS headers in parsed, raw, or combined form across supported formats. |
| `read_hts_index` | table | table | `rduckhts_hts_index` | Inspect high-level HTS index metadata such as sequence names and mapped counts. |
| `read_hts_index_spans` | table_macro | table | `rduckhts_hts_index_spans` | Expand index metadata into span and chunk rows suitable for low-level index inspection. |
| `read_hts_index_raw` | table_macro | table | `rduckhts_hts_index_raw` | Return the raw on-disk HTS index blob together with basic identifying metadata. |

### Compression

| Function | Kind | Returns | R helper | Description |
| --- | --- | --- | --- | --- |
| `bgzip` | table | table | `rduckhts_bgzip` | Compress a plain file to BGZF and return the created output path and byte counts. |
| `bgunzip` | table | table | `rduckhts_bgunzip` | Decompress a BGZF-compressed file and return the created output path and byte counts. |

### Indexing

| Function | Kind | Returns | R helper | Description |
| --- | --- | --- | --- | --- |
| `bam_index` | table | table | `rduckhts_bam_index` | Build a BAM or CRAM index and report the written index path and format. |
| `bcf_index` | table | table | `rduckhts_bcf_index` | Build a TBI or CSI index for a VCF or BCF file and report the written index path and format. |
| `tabix_index` | table | table | `rduckhts_tabix_index` | Build a tabix index for a BGZF-compressed text file using a preset or explicit coordinate columns. |

### Variants

| Function | Kind | Returns | R helper | Description |
| --- | --- | --- | --- | --- |
| `bcftools_liftover` | scalar | STRUCT | `rduckhts_liftover` | Row-oriented liftover kernel intended to mirror bcftools +liftover semantics as closely as possible while returning one STRUCT per input row with fields: src_chrom, src_pos, src_ref, src_alt, dest_chrom, dest_pos, dest_end, dest_ref, dest_alt, mapped, reverse_complemented, swap, reject_reason, and note. Set no_left_align := true to skip post-liftover left-alignment of lifted indels (mirrors --no-left-align in bcftools +liftover). |
| `duckdb_liftover` | table_macro | table | `rduckhts_liftover` | DuckDB-specific wrapper over bcftools_liftover that takes either a table name or a derived-table expression plus column-name strings for chrom/pos/ref/alt and returns the lifted table. The no_left_align parameter mirrors --no-left-align in bcftools +liftover. |
| `bcftools_score` | table | table | `rduckhts_score` | Compute polygenic scores from one genotype BCF/VCF and one summary-statistics file with bcftools +score-compatible GT/DS/HDS/AP/GP/AS dosage semantics, sample subsetting, and region/target/FILTER-string controls. |
| `bcftools_munge_row` | scalar | STRUCT |  | Normalize one summary-statistics row into GWAS-VCF-style fields (chrom/pos/ref/alt/effect metrics), resolving REF/ALT orientation against a FASTA reference and applying swap-aware sign/frequency/count transforms. The output flag `alleles_swapped` means REF/ALT orientation was swapped to match the FASTA reference. |
| `duckdb_munge` | table_macro | table | `rduckhts_munge` | DuckDB macro wrapper over bcftools_munge_row that maps source columns (via preset or explicit map) and returns normalized GWAS-VCF-style rows with lean outputs and explicit `alleles_swapped` semantics. Output columns: chrom, pos, id, ref, alt, alleles_swapped, filter, ns, ez, nc, es, se, lp, af, ac, ne (16 columns). For METAL meta-analysis output with SI/I2/CQ/ED columns, use duckdb_munge_metal. |
| `duckdb_munge_metal` | table_macro | table | `rduckhts_munge` | Extended munge macro with METAL meta-analysis output columns. Same as duckdb_munge but additionally emits: si (imputation info, from INFO input), i2 (Cochran's I² heterogeneity, from HET_I2), cq (Cochran's Q -log10 p, from HET_LP or -log10(HET_P)), and ed (effect direction string, from DIRE; +/- flipped on allele swap). The R wrapper rduckhts_munge() auto-dispatches to this macro when metal keys (INFO, HET_I2, HET_P, HET_LP, DIRE) are present in the resolved column map. |

### Sequence UDFs

| Function | Kind | Returns | R helper | Description |
| --- | --- | --- | --- | --- |
| `seq_revcomp` | scalar | VARCHAR |  | Compute the reverse complement of a DNA sequence using A, C, G, T, and N bases. |
| `seq_canonical` | scalar | VARCHAR |  | Return the lexicographically smaller of a sequence and its reverse complement. |
| `seq_hash_2bit` | scalar | UBIGINT |  | Encode a short DNA sequence as a 2-bit unsigned integer hash. |
| `seq_encode_4bit` | scalar | UTINYINT[] |  | Encode an IUPAC DNA sequence as a list of 4-bit base codes, preserving ambiguity symbols including N. |
| `seq_decode_4bit` | scalar | VARCHAR |  | Decode a list of 4-bit IUPAC DNA base codes back into a sequence string. |
| `seq_gc_content` | scalar | DOUBLE |  | Compute GC fraction for a DNA sequence as a value between 0 and 1. |
| `seq_kmers` | table | table |  | Expand a sequence into positional k-mers with optional canonicalization. |

### SAM Flag UDFs

| Function | Kind | Returns | R helper | Description |
| --- | --- | --- | --- | --- |
| `sam_flag_bits` | scalar | STRUCT |  | Decode a SAM flag into a struct of boolean bit fields using explicit SAM-oriented names such as `is_paired`, `is_proper_pair`, `is_next_segment_unmapped`, and `is_supplementary`. |
| `sam_flag_has` | scalar | BOOLEAN |  | Test whether any bits from the provided SAM flag mask are set in a flag value. |
| `is_forward_aligned` | scalar | BOOLEAN |  | Test whether a mapped segment is aligned to the forward strand. Returns `NULL` for unmapped segments because SAM flag `0x10` does not define genomic strand when `0x4` is set. |
| `is_paired` | scalar | BOOLEAN |  | Test whether the SAM flag indicates that the template has multiple segments in sequencing (`0x1`). |
| `is_proper_pair` | scalar | BOOLEAN |  | Test whether the SAM flag indicates that each segment is properly aligned according to the aligner (`0x2`). |
| `is_unmapped` | scalar | BOOLEAN |  | Test whether the read itself is unmapped according to the SAM flag. |
| `is_next_segment_unmapped` | scalar | BOOLEAN |  | Test whether the next segment in the template is flagged as unmapped (`0x8`). |
| `is_reverse_complemented` | scalar | BOOLEAN |  | Test whether `SEQ` is stored reverse complemented (`0x10`); for mapped reads this corresponds to reverse-strand alignment. |
| `is_next_segment_reverse_complemented` | scalar | BOOLEAN |  | Test whether `SEQ` of the next segment in the template is stored reverse complemented (`0x20`). |
| `is_first_segment` | scalar | BOOLEAN |  | Test whether the read is marked as the first segment in the template. |
| `is_last_segment` | scalar | BOOLEAN |  | Test whether the read is marked as the last segment in the template. |
| `is_secondary` | scalar | BOOLEAN |  | Test whether the alignment is marked as secondary. |
| `is_qc_fail` | scalar | BOOLEAN |  | Test whether the read failed vendor or pipeline quality checks. |
| `is_duplicate` | scalar | BOOLEAN |  | Test whether the alignment is flagged as a duplicate. |
| `is_supplementary` | scalar | BOOLEAN |  | Test whether the alignment is marked as supplementary. |

### CIGAR Utils

| Function | Kind | Returns | R helper | Description |
| --- | --- | --- | --- | --- |
| `cigar_has_soft_clip` | scalar | BOOLEAN |  | Test whether a CIGAR string contains any soft-clipped segment (`S`). |
| `cigar_has_hard_clip` | scalar | BOOLEAN |  | Test whether a CIGAR string contains any hard-clipped segment (`H`). |
| `cigar_left_soft_clip` | scalar | BIGINT |  | Return the left-end soft-clipped length from a CIGAR string, or zero if the alignment does not start with `S`. |
| `cigar_right_soft_clip` | scalar | BIGINT |  | Return the right-end soft-clipped length from a CIGAR string, or zero if the alignment does not end with `S`. |
| `cigar_query_length` | scalar | BIGINT |  | Return the query-consuming length from a CIGAR string, counting `M`, `I`, `S`, `=`, and `X`. |
| `cigar_aligned_query_length` | scalar | BIGINT |  | Return the aligned query length from a CIGAR string, counting `M`, `=`, and `X` but excluding clips and insertions. |
| `cigar_reference_length` | scalar | BIGINT |  | Return the reference-consuming length from a CIGAR string, counting `M`, `D`, `N`, `=`, and `X`. |
| `cigar_has_op` | scalar | BOOLEAN |  | Test whether a CIGAR string contains at least one instance of the requested operator. |

