331 lines
11 KiB
Python
331 lines
11 KiB
Python
# Authors: Andreas Mueller <andreas.mueller@columbia.edu>
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# Guillaume Lemaitre <guillaume.lemaitre@inria.fr>
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# License: BSD 3 clause
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import warnings
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import numpy as np
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from ..base import BaseEstimator, RegressorMixin, clone
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from ..utils.validation import check_is_fitted
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from ..utils._tags import _safe_tags
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from ..utils import check_array, _safe_indexing
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from ..utils._param_validation import HasMethods
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from ..preprocessing import FunctionTransformer
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from ..exceptions import NotFittedError
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__all__ = ["TransformedTargetRegressor"]
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class TransformedTargetRegressor(RegressorMixin, BaseEstimator):
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"""Meta-estimator to regress on a transformed target.
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Useful for applying a non-linear transformation to the target `y` in
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regression problems. This transformation can be given as a Transformer
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such as the :class:`~sklearn.preprocessing.QuantileTransformer` or as a
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function and its inverse such as `np.log` and `np.exp`.
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The computation during :meth:`fit` is::
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regressor.fit(X, func(y))
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or::
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regressor.fit(X, transformer.transform(y))
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The computation during :meth:`predict` is::
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inverse_func(regressor.predict(X))
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or::
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transformer.inverse_transform(regressor.predict(X))
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Read more in the :ref:`User Guide <transformed_target_regressor>`.
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.. versionadded:: 0.20
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Parameters
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----------
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regressor : object, default=None
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Regressor object such as derived from
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:class:`~sklearn.base.RegressorMixin`. This regressor will
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automatically be cloned each time prior to fitting. If `regressor is
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None`, :class:`~sklearn.linear_model.LinearRegression` is created and used.
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transformer : object, default=None
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Estimator object such as derived from
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:class:`~sklearn.base.TransformerMixin`. Cannot be set at the same time
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as `func` and `inverse_func`. If `transformer is None` as well as
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`func` and `inverse_func`, the transformer will be an identity
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transformer. Note that the transformer will be cloned during fitting.
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Also, the transformer is restricting `y` to be a numpy array.
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func : function, default=None
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Function to apply to `y` before passing to :meth:`fit`. Cannot be set
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at the same time as `transformer`. The function needs to return a
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2-dimensional array. If `func is None`, the function used will be the
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identity function.
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inverse_func : function, default=None
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Function to apply to the prediction of the regressor. Cannot be set at
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the same time as `transformer`. The function needs to return a
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2-dimensional array. The inverse function is used to return
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predictions to the same space of the original training labels.
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check_inverse : bool, default=True
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Whether to check that `transform` followed by `inverse_transform`
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or `func` followed by `inverse_func` leads to the original targets.
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Attributes
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----------
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regressor_ : object
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Fitted regressor.
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transformer_ : object
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Transformer used in :meth:`fit` and :meth:`predict`.
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n_features_in_ : int
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Number of features seen during :term:`fit`. Only defined if the
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underlying regressor exposes such an attribute when fit.
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.. versionadded:: 0.24
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feature_names_in_ : ndarray of shape (`n_features_in_`,)
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Names of features seen during :term:`fit`. Defined only when `X`
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has feature names that are all strings.
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.. versionadded:: 1.0
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See Also
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--------
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sklearn.preprocessing.FunctionTransformer : Construct a transformer from an
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arbitrary callable.
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Notes
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-----
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Internally, the target `y` is always converted into a 2-dimensional array
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to be used by scikit-learn transformers. At the time of prediction, the
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output will be reshaped to a have the same number of dimensions as `y`.
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See :ref:`examples/compose/plot_transformed_target.py
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<sphx_glr_auto_examples_compose_plot_transformed_target.py>`.
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Examples
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--------
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>>> import numpy as np
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>>> from sklearn.linear_model import LinearRegression
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>>> from sklearn.compose import TransformedTargetRegressor
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>>> tt = TransformedTargetRegressor(regressor=LinearRegression(),
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... func=np.log, inverse_func=np.exp)
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>>> X = np.arange(4).reshape(-1, 1)
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>>> y = np.exp(2 * X).ravel()
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>>> tt.fit(X, y)
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TransformedTargetRegressor(...)
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>>> tt.score(X, y)
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1.0
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>>> tt.regressor_.coef_
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array([2.])
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"""
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_parameter_constraints: dict = {
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"regressor": [HasMethods(["fit", "predict"]), None],
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"transformer": [HasMethods("transform"), None],
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"func": [callable, None],
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"inverse_func": [callable, None],
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"check_inverse": ["boolean"],
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}
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def __init__(
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self,
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regressor=None,
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*,
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transformer=None,
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func=None,
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inverse_func=None,
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check_inverse=True,
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):
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self.regressor = regressor
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self.transformer = transformer
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self.func = func
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self.inverse_func = inverse_func
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self.check_inverse = check_inverse
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def _fit_transformer(self, y):
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"""Check transformer and fit transformer.
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Create the default transformer, fit it and make additional inverse
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check on a subset (optional).
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"""
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if self.transformer is not None and (
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self.func is not None or self.inverse_func is not None
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):
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raise ValueError(
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"'transformer' and functions 'func'/'inverse_func' cannot both be set."
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)
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elif self.transformer is not None:
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self.transformer_ = clone(self.transformer)
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else:
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if self.func is not None and self.inverse_func is None:
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raise ValueError(
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"When 'func' is provided, 'inverse_func' must also be provided"
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)
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self.transformer_ = FunctionTransformer(
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func=self.func,
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inverse_func=self.inverse_func,
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validate=True,
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check_inverse=self.check_inverse,
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)
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# XXX: sample_weight is not currently passed to the
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# transformer. However, if transformer starts using sample_weight, the
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# code should be modified accordingly. At the time to consider the
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# sample_prop feature, it is also a good use case to be considered.
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self.transformer_.fit(y)
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if self.check_inverse:
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idx_selected = slice(None, None, max(1, y.shape[0] // 10))
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y_sel = _safe_indexing(y, idx_selected)
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y_sel_t = self.transformer_.transform(y_sel)
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if not np.allclose(y_sel, self.transformer_.inverse_transform(y_sel_t)):
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warnings.warn(
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"The provided functions or transformer are"
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" not strictly inverse of each other. If"
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" you are sure you want to proceed regardless"
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", set 'check_inverse=False'",
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UserWarning,
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)
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def fit(self, X, y, **fit_params):
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"""Fit the model according to the given training data.
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Parameters
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----------
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X : {array-like, sparse matrix} of shape (n_samples, n_features)
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Training vector, where `n_samples` is the number of samples and
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`n_features` is the number of features.
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y : array-like of shape (n_samples,)
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Target values.
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**fit_params : dict
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Parameters passed to the `fit` method of the underlying
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regressor.
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Returns
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-------
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self : object
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Fitted estimator.
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"""
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self._validate_params()
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if y is None:
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raise ValueError(
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f"This {self.__class__.__name__} estimator "
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"requires y to be passed, but the target y is None."
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)
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y = check_array(
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y,
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input_name="y",
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accept_sparse=False,
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force_all_finite=True,
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ensure_2d=False,
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dtype="numeric",
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allow_nd=True,
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)
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# store the number of dimension of the target to predict an array of
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# similar shape at predict
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self._training_dim = y.ndim
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# transformers are designed to modify X which is 2d dimensional, we
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# need to modify y accordingly.
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if y.ndim == 1:
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y_2d = y.reshape(-1, 1)
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else:
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y_2d = y
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self._fit_transformer(y_2d)
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# transform y and convert back to 1d array if needed
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y_trans = self.transformer_.transform(y_2d)
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# FIXME: a FunctionTransformer can return a 1D array even when validate
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# is set to True. Therefore, we need to check the number of dimension
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# first.
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if y_trans.ndim == 2 and y_trans.shape[1] == 1:
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y_trans = y_trans.squeeze(axis=1)
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if self.regressor is None:
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from ..linear_model import LinearRegression
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self.regressor_ = LinearRegression()
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else:
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self.regressor_ = clone(self.regressor)
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self.regressor_.fit(X, y_trans, **fit_params)
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if hasattr(self.regressor_, "feature_names_in_"):
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self.feature_names_in_ = self.regressor_.feature_names_in_
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return self
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def predict(self, X, **predict_params):
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"""Predict using the base regressor, applying inverse.
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The regressor is used to predict and the `inverse_func` or
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`inverse_transform` is applied before returning the prediction.
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Parameters
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----------
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X : {array-like, sparse matrix} of shape (n_samples, n_features)
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Samples.
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**predict_params : dict of str -> object
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Parameters passed to the `predict` method of the underlying
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regressor.
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Returns
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-------
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y_hat : ndarray of shape (n_samples,)
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Predicted values.
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"""
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check_is_fitted(self)
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pred = self.regressor_.predict(X, **predict_params)
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if pred.ndim == 1:
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pred_trans = self.transformer_.inverse_transform(pred.reshape(-1, 1))
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else:
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pred_trans = self.transformer_.inverse_transform(pred)
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if (
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self._training_dim == 1
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and pred_trans.ndim == 2
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and pred_trans.shape[1] == 1
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):
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pred_trans = pred_trans.squeeze(axis=1)
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return pred_trans
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def _more_tags(self):
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regressor = self.regressor
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if regressor is None:
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from ..linear_model import LinearRegression
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regressor = LinearRegression()
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return {
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"poor_score": True,
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"multioutput": _safe_tags(regressor, key="multioutput"),
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}
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@property
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def n_features_in_(self):
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"""Number of features seen during :term:`fit`."""
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# For consistency with other estimators we raise a AttributeError so
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# that hasattr() returns False the estimator isn't fitted.
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try:
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check_is_fitted(self)
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except NotFittedError as nfe:
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raise AttributeError(
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"{} object has no n_features_in_ attribute.".format(
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self.__class__.__name__
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)
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) from nfe
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return self.regressor_.n_features_in_
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