feat: add compute_variation_ratios tool

Port compute_variation_ratios.py from human-diversity-reference/scripts as
a defopt-compatible toolkit tool. Counts per-sample non-reference variant
sites above each of seven predefined gnomAD population frequency thresholds
and writes a sample-level Hail table with population labels and counts.
Removes the debug pprint call present in the original.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ameynert

divref/divref/tools/compute_variation_ratios.py

@@ -0,0 +1,51 @@
+"""Tool to compute per-sample variant site counts across gnomAD frequency thresholds."""
+
+import hail as hl
+
+from divref.haplotype import HailPath
+
+_FREQ_THRESHOLDS = [0, 0.0001, 0.001, 0.005, 0.01, 0.05, 0.1]
+
+
+def compute_variation_ratios(
+    *,
+    vcfs_path: HailPath,
+    gnomad_va_file: HailPath,
+    gnomad_sa_file: HailPath,
+    output_ht: HailPath,
+) -> None:
+    """
+    Compute per-sample counts of non-reference variant sites across frequency thresholds.
+
+    For each sample and each predefined gnomAD population frequency threshold, counts
+    the number of sites where the sample carries a non-reference genotype. Writes a
+    sample-level Hail table with population labels and per-threshold site counts.
+
+    Args:
+        vcfs_path: Path or glob pattern to input VCF files (GRCh38).
+        gnomad_va_file: Path to the gnomAD variant annotations Hail table
+            (from extract_gnomad_afs).
+        gnomad_sa_file: Path to the gnomAD sample metadata Hail table
+            (from extract_gnomad_afs).
+        output_ht: Output path for the sample-level Hail table.
+    """
+    hl.init()
+
+    gnomad_sa = hl.read_table(gnomad_sa_file)
+    gnomad_va = hl.read_table(gnomad_va_file)
+
+    mt = hl.import_vcf(vcfs_path, reference_genome="GRCh38", min_partitions=64)
+    mt = mt.select_rows().select_cols()
+    mt = mt.annotate_rows(freq=gnomad_va[mt.row_key].pop_freqs)
+    mt = mt.filter_rows(hl.is_defined(mt.freq))
+    mt = mt.annotate_rows(max_pop_freq=hl.max(mt.freq.map(lambda x: hl.max(x.AF))))
+
+    mt = mt.annotate_cols(pop=gnomad_sa[mt.col_key].pop)
+    mt = mt.annotate_cols(
+        counts=hl.struct(**{
+            f"n_sites_above_{x}": hl.agg.count_where(mt.GT.is_non_ref() & (mt.max_pop_freq > x))
+            for x in _FREQ_THRESHOLDS
+        })
+    )
+
+    mt.cols().write(output_ht, overwrite=True)