PCC

class mlquantify.counting.PCC(estimator=None)

Probabilistic Classify and Count (PCC) quantifier.

Targets prior probability shift. Estimates class prevalences by averaging the posterior probabilities returned by a probabilistic classifier over all test instances. Generally less biased than CC, but, lacking any error correction, it still drifts under strong shift and assumes a well-calibrated classifier.

Parameters:

estimatorestimator, optional

A classifier with fit and predict_proba methods. If None, call aggregate directly.

Attributes:

estimator_estimator

The fitted underlying classifier.

classes_ndarray of shape (n_classes,)

Class labels seen during fit.

See also

CC

Classify and Count quantifier.

ACC

Adjusted Classify and Count quantifier.

GPACC

Multiclass, corrected generalisation of PCC.

Notes

PCC is unbiased under prior shift only when the posteriors are well calibrated on the test distribution; calibration drift re-introduces bias. It applies no explicit correction for classifier error.

References

References

[1]

Bella, A., Ferri, C., Hernández-Orallo, J., & Ramírez-Quintana, M. J. (2010). Quantification via Probability Estimators. ICDM, pp. 737–742.

[2]

Forman, G. (2005). Counting Positives Accurately Despite Inaccurate Classification. ECML, pp. 564–575.

Examples

>>> from mlquantify.counting import PCC
>>> from sklearn.linear_model import LogisticRegression
>>> import numpy as np
>>> X, y = np.random.randn(100, 5), np.random.randint(0, 2, 100)
>>> q = PCC(LogisticRegression()).fit(X, y)
>>> q.predict(X)
{0: ..., 1: ...}
>>> # call aggregate directly with pre-computed posterior probabilities
>>> proba = q.estimator_.predict_proba(X)
>>> q.aggregate(proba)
{0: ..., 1: ...}

aggregate(predictions, classes=None)

Aggregate predictions into class prevalence estimates.

Parameters:

predictionsndarray of shape (n_samples, n_classes)

Estimator predictions on test data. Can be probabilities (n_samples, n_classes) or class labels (n_samples,).

classesarray-like of shape (n_classes,) or None, default=None

Class labels the output must report, in order. When given, every class appears in the result even if absent from predictions (with prevalence 0). When None, the classes seen during fit are used; if the quantifier is unfitted, they are inferred from the predictions (categorical) or their width (probabilities).

Returns:

ndarray of shape (n_classes,)

Class prevalence estimates.

Examples

>>> from mlquantify.counting import PCC
>>> import numpy as np
>>> q = PCC()
>>> predictions = np.random.rand(200, 2)
>>> q.aggregate(predictions)
{0: ..., 1: ...}

fit(X, y, estimator_fitted=False, *args, **kwargs)

Fit the quantifier using the provided data and estimator.

get_metadata_routing()

Get metadata routing of this object.

Please check User Guide on how the routing mechanism works.

Returns:

routingMetadataRequest

A MetadataRequest encapsulating routing information.

get_params(deep=True)

Get parameters for this estimator.

Parameters:

deepbool, default=True

If True, will return the parameters for this estimator and contained subobjects that are estimators.

Returns:

paramsdict

Parameter names mapped to their values.

predict(X)

Predict class prevalences for the given data.

save_quantifier(path: str | None = None) → None

Save the quantifier instance to a file.

set_fit_request(*, estimator_fitted: bool | None | str = '$UNCHANGED$') → PCC

Configure whether metadata should be requested to be passed to the fit method.

Note that this method is only relevant when this estimator is used as a sub-estimator within a meta-estimator and metadata routing is enabled with enable_metadata_routing=True (see sklearn.set_config). Please check the User Guide on how the routing mechanism works.

The options for each parameter are:

• True: metadata is requested, and passed to fit if provided. The request is ignored if metadata is not provided.

• False: metadata is not requested and the meta-estimator will not pass it to fit.

• None: metadata is not requested, and the meta-estimator will raise an error if the user provides it.

• str: metadata should be passed to the meta-estimator with this given alias instead of the original name.

The default (sklearn.utils.metadata_routing.UNCHANGED) retains the existing request. This allows you to change the request for some parameters and not others.

Added in version 1.3.

Parameters:

estimator_fittedstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED

Metadata routing for estimator_fitted parameter in fit.

Returns:

selfobject

The updated object.

set_params(**params)

Set the parameters of this estimator.

The method works on simple estimators as well as on nested objects (such as Pipeline). The latter have parameters of the form <component>__<parameter> so that it’s possible to update each component of a nested object.

Parameters:

**paramsdict

Estimator parameters.

Returns:

selfestimator instance

Estimator instance.