scatac-preprocessing

scatac-preprocessing

When to use

The user has a peak × cell scATAC AnnData (raw-count-like accessibility matrix in .X) and wants the standard "filter → TF-IDF → LSI → graph → UMAP → Leiden" pipeline in one shot. Currently a single backend: tfidf_lsi (Signac-style). The skill stops at clustered UMAP — no fragment QC, no peak calling, no motif / gene-activity scoring, no multi-sample integration. For scRNA preprocessing use sc-preprocessing.

Inputs & Outputs

Flow

1. Load the peak × cell input via the shared smart_load (AnnData / 10x H5 / loom / CSV / 10x dir).
2. Validate .X is present, non-empty, non-negative.
3. Compute per-cell n_peaks_by_counts / total_counts; filter cells by --min-peaks and peaks by --min-cells.
4. Retain the globally most accessible peaks up to --n-top-peaks.
5. Run Signac-style TF-IDF (--tfidf-scale-factor); truncated-SVD LSI to --n-lsi components.
6. Build neighbour graph (--n-neighbors), UMAP, Leiden (--leiden-resolution).
7. Save processed.h5ad, tables, figures, report.md, result.json.

Gotchas

• Filtering can wipe everything. scatac_preprocessing.py:149 raises RuntimeError("All cells were removed by min_peaks. Lower the threshold.") and :154 raises RuntimeError("All peaks were removed by min_cells. Lower the threshold.") — both are hard fails. Inspect n_peaks_by_counts distribution before tightening these thresholds; --min-peaks 200 (default) assumes a typical 10x scATAC depth.
• LSI hard-fails on a degenerate matrix. scatac_preprocessing.py:228 raises RuntimeError("Not enough cells or peaks remain to compute a stable LSI embedding.") when the matrix is too sparse / small after filtering. Either lower QC thresholds or feed a richer dataset.
• Input must be non-negative count-like in .X. scatac_preprocessing.py:118 raises ValueError("Input AnnData has no matrix in adata.X."); :122 raises ValueError("Input matrix is empty."); :124 raises ValueError("scATAC preprocessing requires a non-negative accessibility matrix."). Already-TF-IDF-transformed data will fail the non-negativity check.
• processed.h5ad keeps only retained peaks. scatac_preprocessing.py:176 does adata = adata[:, keep].copy() — var is filtered to the top n_top_peaks accessible. The original peak universe is not preserved in X (the deleted peaks are gone). Snapshot the input before running if you need the full peak space later.
• --input mandatory unless --demo. scatac_preprocessing.py:809 raises ValueError("--input required when not using --demo").
• Single backend only. scatac_preprocessing.py:272 raises ValueError(f"Unknown preprocessing method '{method}'") for anything other than tfidf_lsi. The --method flag exists for forward compatibility; today it's effectively a no-op.

Key CLI

# Demo (built-in synthetic scATAC)
python omicsclaw.py run scatac-preprocessing --demo --output /tmp/scatac_demo

# Standard run on a 10x scATAC h5
python omicsclaw.py run scatac-preprocessing \
  --input atac_peaks.h5 --output results/

# Tune QC + feature budget
python omicsclaw.py run scatac-preprocessing \
  --input atac_peaks.h5ad --output results/ \
  --min-peaks 300 --min-cells 10 --n-top-peaks 20000

# Tune latent space + clustering
python omicsclaw.py run scatac-preprocessing \
  --input atac_peaks.h5ad --output results/ \
  --n-lsi 40 --n-neighbors 20 --leiden-resolution 1.0

See also

• references/parameters.md — every CLI flag, per-method tunables
• references/methodology.md — TF-IDF + LSI math; Signac alignment
• references/output_contract.md — obsm/var schema + table layouts
• Adjacent skills: sc-preprocessing (parallel — scRNA, NOT scATAC), sc-clustering (downstream — re-cluster on obsm["X_lsi"] if you want a different resolution without re-running TF-IDF)