MaldiBatchKit

Batch-effect correction methods for MALDI-TOF spectra in clinical AMR prediction workflows

Installation • Features • Quick Start • Algorithms • Diagnostics • MaldiSuite • Citation

MaldiBatchKit is part of the MaldiSuite ecosystem and complements MaldiAMRKit: where MaldiAMRKit handles preprocessing, alignment and AMR-aware evaluation, MaldiBatchKit focuses on the harmonization step, removing the inter-batch / inter-site shifts that plague multi-centre MALDI-TOF studies.

Installation

pip install maldibatchkit

Optional extras:

pip install maldibatchkit[viz]      # UMAP plots, seaborn
pip install maldibatchkit[dev]      # testing + linting
pip install maldibatchkit[docs]     # sphinx

maldiamrkit is a core dependency - installing MaldiBatchKit pulls it in automatically. BatchAwareWarping reuses maldiamrkit.alignment.Warping under the hood, and the MaldiSetAdapter bridges to maldiamrkit.MaldiSet for end-to-end AMR workflows.

Install the full MaldiSuite

To install MaldiBatchKit together with MaldiAMRKit and MaldiDeepKit at compatible versions, install the maldisuite meta-package:

pip install maldisuite

Visit the MaldiSuite landing page at https://ettorerocchi.github.io/MaldiSuite/.

Features

• Unified sklearn API (BaseEstimator + TransformerMixin) for every correction method. batch and covariates are passed at construction time and aligned to X.index at fit / transform, so the same object works inside Pipeline / cross-validation without data leakage.
• ComBat variants (Johnson 2007, Fortin 2018, Chen 2022 CovBat) re-exported from combatlearn.
• Limma removeBatchEffect (Ritchie et al. 2015).
• Harmony (Korsunsky et al. 2019) via harmonypy, with a mandatory, frozen PCA preprocessing stage so it behaves sensibly on high-dimensional MALDI-TOF intensity matrices (tune with the n_components= argument).
• Simple baselines: median centering, z-score per batch, reference scaling.
• MALDI-specific corrections:
  • BatchAwareWarping - per-batch m/z warping sharing a global reference (wraps maldiamrkit.alignment.Warping).
  • QualityWeightedComBat - weighted empirical-Bayes ComBat variant where low-SNR spectra contribute less to the shrinkage prior.
  • SpeciesAwareComBat - convenience preset for ComBat-Fortin with species as the protected biological covariate.
• Diagnostics: kBET, LISI, silhouette-by-batch, per-batch peak drift, per-batch TIC coefficient of variation, per-batch spectrum count, plus a combined diagnostic_report DataFrame summary.
• Visualization: UMAP before/after, per-batch peak-shape overlays, before/after bar charts.
• Integration adapter: MaldiSetAdapter turns a maldiamrkit.MaldiSet into a corrected MaldiSet in one call.
• CLI: maldibatchkit correct ... and maldibatchkit diagnose ....

Quick start

from maldibatchkit import ComBat, QualityWeightedComBat, SpeciesAwareComBat
from maldibatchkit.diagnostics import diagnostic_report

# X: (n_samples, n_bins) DataFrame; batch & species indexed by X.index
corrector = SpeciesAwareComBat(batch=batch, species=species)
X_corrected = corrector.fit_transform(X)

report = diagnostic_report(X, X_corrected, batch)
print(report)

Train/test without leakage:

from sklearn.model_selection import train_test_split

X_train, X_test, y_train, y_test = train_test_split(X, y, stratify=batch)

corrector = ComBat(batch=batch, method="fortin", discrete_covariates=species)
corrector.fit(X_train)              # learns on train only
X_train_c = corrector.transform(X_train)
X_test_c  = corrector.transform(X_test)   # same parameters applied to test

batch is indexed by the same sample IDs that X uses, so the corrector picks the right subset on each call.

MaldiSet integration

from maldiamrkit import MaldiSet
from maldibatchkit.integrations import MaldiSetAdapter
from maldibatchkit import SpeciesAwareComBat

ds = MaldiSet.from_directory(...)
adapter = MaldiSetAdapter(
    batch_column="Batch",
    species_column="Species",
    quality_column="SNR",
)
corrected_ds = adapter.correct(ds, SpeciesAwareComBat)
corrected_ds.X      # harmonised feature matrix
corrected_ds.y      # AMR labels, unchanged

CLI

The CLI is organised as maldibatchkit correct <method> + maldibatchkit diagnose. Every method has its own subcommand with only the flags it actually uses:

# Vanilla Johnson ComBat
maldibatchkit correct combat \
    -i X.csv --batch-csv batch.csv -o X_corrected.csv

# Fortin ComBat with a species covariate
maldibatchkit correct combat-fortin \
    -i X.csv --batch-csv batch.csv \
    --discrete-covariates-csv species.csv \
    -o X_corrected.csv

# Species-aware preset (shortcut for the above)
maldibatchkit correct species-combat \
    -i X.csv --batch-csv batch.csv --species-csv species.csv \
    -o X_corrected.csv

# Quality-weighted ComBat
maldibatchkit correct quality-combat \
    -i X.csv --batch-csv batch.csv --quality-csv snr.csv \
    -o X_corrected.csv

# Diagnostic report
maldibatchkit diagnose \
    -i X.csv --corrected X_corrected.csv \
    --batch-csv batch.csv --mz-csv mz.csv -o report.csv

NPZ inputs bundle X, index, columns, and batch labels in one file, so the same commands work without sidecar CSVs:

maldibatchkit correct combat-fortin \
    -i maldiset.npz \
    --discrete-covariates-csv species.csv \
    -o corrected.npz

Run maldibatchkit correct <method> --help for the full flag list of any corrector. combat-fortin / combat-chen refuse to run without covariates (they would silently reduce to Johnson ComBat); species-combat / quality-combat require their dedicated --species-csv / --quality-csv inputs.

Algorithms

Method	Class	Protects covariates?	Train/test safe?
ComBat (Johnson, Fortin, Chen)	ComBat	Fortin / Chen	yes
Limma	Limma	via design=	yes
Harmony	Harmony	via covariates=	yes
Median centering	MedianCentering	no	yes
Z-score per batch	ZScorePerBatch	no	yes
Reference scaling	ReferenceScaling	no	yes
Batch-aware warping	BatchAwareWarping	no	yes
Quality-weighted ComBat	QualityWeightedComBat	no	yes
Species-aware ComBat	SpeciesAwareComBat	species	yes

See the QualityWeightedComBat docstring for the mathematical formulation of the weighted empirical-Bayes update.

Extending MaldiBatchKit

Every corrector in this package inherits from BaseBatchCorrector, which is re-exported at the top level. Subclass it, implement _fit_impl and _transform_impl, and you get a scikit-learn compatible, train/test-safe corrector for free - the base class handles index alignment between X and the stored batch labels, NaN / finite checks, DataFrame-vs-ndarray round-tripping, and the feature_names_in_ / n_features_in_ / get_feature_names_out sklearn bookkeeping.

Minimal custom corrector:

import pandas as pd
from maldibatchkit import BaseBatchCorrector

class MeanCentering(BaseBatchCorrector):
    """Subtract per-batch means from each feature."""

    def _fit_impl(self, X_df, batch):
        # Store whatever you learn as ``..._`` attributes so
        # ``sklearn.utils.validation.check_is_fitted`` picks them up.
        self.batch_means_ = X_df.groupby(batch).mean()
        self.grand_mean_ = X_df.mean(axis=0)

    def _transform_impl(self, X_df, batch):
        out = X_df.copy().astype(float)
        known = set(self.batch_means_.index)
        for lvl in pd.unique(batch):
            mask = batch == lvl
            offset = (
                self.batch_means_.loc[lvl].to_numpy()
                if lvl in known
                else self.grand_mean_.to_numpy()   # unseen-batch fallback
            )
            out.loc[mask] = out.loc[mask].to_numpy() - offset
        return out

Drop it straight into a pipeline:

from sklearn.pipeline import Pipeline
from sklearn.preprocessing import StandardScaler
from sklearn.ensemble import RandomForestClassifier

pipe = Pipeline([
    ("mean", MeanCentering(batch=batch)),
    ("scaler", StandardScaler()),
    ("clf", RandomForestClassifier()),
])
pipe.fit(X_train, y_train)
pipe.score(X_test, y_test)       # no leakage: transform, never refit

Conventions (see CONTRIBUTING.md):

• NumPy-style docstring on every public class.
• Fitted attributes end in _ (self.batch_means_, not self.means).
• transform must be idempotent - no side effects outside fit.
• Raise a clear ImportError (not a bare ModuleNotFoundError) when an optional dependency is missing; see Harmony._require_harmonypy for the reference pattern.

Look at maldibatchkit/corrections/baselines.py for the simplest end-to-end references (MedianCentering, ZScorePerBatch, ReferenceScaling), or at quality_weighted.py for a corrector with an iterative fit.

Diagnostics

from maldibatchkit.diagnostics import (
    silhouette_batch, kbet, lisi,
    peak_position_drift, tic_cov_per_batch, per_batch_spectrum_count,
    diagnostic_report,
)

All metrics take the same (X, batch) signature. diagnostic_report composes them into a tidy DataFrame suitable for plot_diagnostic_summary.

MaldiSuite Ecosystem

MaldiBatchKit is the harmonisation package of the MaldiSuite ecosystem:

• MaldiAMRKit - data model (MaldiSpectrum, MaldiSet), preprocessing, alignment, peak detection, differential analysis, and AMR-aware evaluation.
• MaldiBatchKit (this package) - batch-effect correction and harmonisation for multi-centre / multi-instrument MALDI-TOF spectra.
• MaldiDeepKit - sklearn-compatible deep learning classifiers (MLP, CNN, ResNet, Transformer).

The three packages share the MaldiSet / MaldiSpectrum data model and are designed to compose in a single end-to-end pipeline. Install the full suite with pip install maldisuite. Landing page: MaldiSuite.

Citation

If you use MaldiBatchKit in academic work please cite:

Citation will be available soon.

along with the upstream references for whichever methods you apply (Johnson 2007, Fortin 2018, Chen 2022, Ritchie 2015, Korsunsky 2019).

License

MIT. See LICENSE.