QuaPy/quapy/classification/methods.py

98 lines
4.0 KiB
Python

from sklearn.base import BaseEstimator
from sklearn.decomposition import TruncatedSVD
from sklearn.linear_model import LogisticRegression
class LowRankLogisticRegression(BaseEstimator):
"""
An example of a classification method (i.e., an object that implements `fit`, `predict`, and `predict_proba`)
that also generates embedded inputs (i.e., that implements `transform`), as those required for
:class:`quapy.method.neural.QuaNet`. This is a mock method to allow for easily instantiating
:class:`quapy.method.neural.QuaNet` on array-like real-valued instances.
The transformation consists of applying :class:`sklearn.decomposition.TruncatedSVD`
while classification is performed using :class:`sklearn.linear_model.LogisticRegression` on the low-rank space.
:param n_components: the number of principal components to retain
:param kwargs: parameters for the
`Logistic Regression <https://scikit-learn.org/stable/modules/generated/sklearn.linear_model.LogisticRegression.html>`__ classifier
"""
def __init__(self, n_components=100, **kwargs):
self.n_components = n_components
self.learner = LogisticRegression(**kwargs)
def get_params(self):
"""
Get hyper-parameters for this estimator.
:return: a dictionary with parameter names mapped to their values
"""
params = {'n_components': self.n_components}
params.update(self.learner.get_params())
return params
def set_params(self, **params):
"""
Set the parameters of this estimator.
:param parameters: a `**kwargs` dictionary with the estimator parameters for
`Logistic Regression <https://scikit-learn.org/stable/modules/generated/sklearn.linear_model.LogisticRegression.html>`__
and eventually also `n_components` for `TruncatedSVD`
"""
params_ = dict(params)
if 'n_components' in params_:
self.n_components = params_['n_components']
del params_['n_components']
self.learner.set_params(**params_)
def fit(self, X, y):
"""
Fit the model according to the given training data. The fit consists of
fitting `TruncatedSVD` and then `LogisticRegression` on the low-rank representation.
:param X: array-like of shape `(n_samples, n_features)` with the instances
:param y: array-like of shape `(n_samples, n_classes)` with the class labels
:return: `self`
"""
nF = X.shape[1]
self.pca = None
if nF > self.n_components:
self.pca = TruncatedSVD(self.n_components).fit(X)
X = self.transform(X)
self.learner.fit(X, y)
self.classes_ = self.learner.classes_
return self
def predict(self, X):
"""
Predicts labels for the instances `X` embedded into the low-rank space.
:param X: array-like of shape `(n_samples, n_features)` instances to classify
:return: a `numpy` array of length `n` containing the label predictions, where `n` is the number of
instances in `X`
"""
X = self.transform(X)
return self.learner.predict(X)
def predict_proba(self, X):
"""
Predicts posterior probabilities for the instances `X` embedded into the low-rank space.
:param X: array-like of shape `(n_samples, n_features)` instances to classify
:return: array-like of shape `(n_samples, n_classes)` with the posterior probabilities
"""
X = self.transform(X)
return self.learner.predict_proba(X)
def transform(self, X):
"""
Returns the low-rank approximation of `X` with `n_components` dimensions, or `X` unaltered if
`n_components` >= `X.shape[1]`.
:param X: array-like of shape `(n_samples, n_features)` instances to embed
:return: array-like of shape `(n_samples, n_components)` with the embedded instances
"""
if self.pca is None:
return X
return self.pca.transform(X)