githubmirror/scikit-learn

sklearn/base.py
1 068 строк38 KB
Christian Veenhuis
DOC unify usage of 'w.r.t.' (#25683)
08 мар 2023, 19:21
08 мар 2023, 19:21cc4984f
"""Base classes for all estimators."""

# Author: Gael Varoquaux <gael.varoquaux@normalesup.org>
# License: BSD 3 clause

import copy
import warnings
from collections import defaultdict
import platform
import inspect
import re

import numpy as np

from . import __version__
from ._config import get_config
from .utils import _IS_32BIT
from .utils._set_output import _SetOutputMixin
from .utils._tags import (
    _DEFAULT_TAGS,
)
from .utils.validation import check_X_y
from .utils.validation import check_array
from .utils.validation import _check_y
from .utils.validation import _num_features
from .utils.validation import _check_feature_names_in
from .utils.validation import _generate_get_feature_names_out
from .utils.validation import check_is_fitted
from .utils.validation import _get_feature_names
from .utils._estimator_html_repr import estimator_html_repr
from .utils._param_validation import validate_parameter_constraints


def clone(estimator, *, safe=True):
    """Construct a new unfitted estimator with the same parameters.

    Clone does a deep copy of the model in an estimator
    without actually copying attached data. It returns a new estimator
    with the same parameters that has not been fitted on any data.

    Parameters
    ----------
    estimator : {list, tuple, set} of estimator instance or a single \
            estimator instance
        The estimator or group of estimators to be cloned.
    safe : bool, default=True
        If safe is False, clone will fall back to a deep copy on objects
        that are not estimators.

    Returns
    -------
    estimator : object
        The deep copy of the input, an estimator if input is an estimator.

    Notes
    -----
    If the estimator's `random_state` parameter is an integer (or if the
    estimator doesn't have a `random_state` parameter), an *exact clone* is
    returned: the clone and the original estimator will give the exact same
    results. Otherwise, *statistical clone* is returned: the clone might
    return different results from the original estimator. More details can be
    found in :ref:`randomness`.
    """
    estimator_type = type(estimator)
    # XXX: not handling dictionaries
    if estimator_type in (list, tuple, set, frozenset):
        return estimator_type([clone(e, safe=safe) for e in estimator])
    elif not hasattr(estimator, "get_params") or isinstance(estimator, type):
        if not safe:
            return copy.deepcopy(estimator)
        else:
            if isinstance(estimator, type):
                raise TypeError(
                    "Cannot clone object. "
                    + "You should provide an instance of "
                    + "scikit-learn estimator instead of a class."
                )
            else:
                raise TypeError(
                    "Cannot clone object '%s' (type %s): "
                    "it does not seem to be a scikit-learn "
                    "estimator as it does not implement a "
                    "'get_params' method." % (repr(estimator), type(estimator))
                )

    klass = estimator.__class__
    new_object_params = estimator.get_params(deep=False)
    for name, param in new_object_params.items():
        new_object_params[name] = clone(param, safe=False)
    new_object = klass(**new_object_params)
    params_set = new_object.get_params(deep=False)

    # quick sanity check of the parameters of the clone
    for name in new_object_params:
        param1 = new_object_params[name]
        param2 = params_set[name]
        if param1 is not param2:
            raise RuntimeError(
                "Cannot clone object %s, as the constructor "
                "either does not set or modifies parameter %s" % (estimator, name)
            )

    # _sklearn_output_config is used by `set_output` to configure the output
    # container of an estimator.
    if hasattr(estimator, "_sklearn_output_config"):
        new_object._sklearn_output_config = copy.deepcopy(
            estimator._sklearn_output_config
        )
    return new_object


class BaseEstimator:
    """Base class for all estimators in scikit-learn.

    Notes
    -----
    All estimators should specify all the parameters that can be set
    at the class level in their ``__init__`` as explicit keyword
    arguments (no ``*args`` or ``**kwargs``).
    """

    @classmethod
    def _get_param_names(cls):
        """Get parameter names for the estimator"""
        # fetch the constructor or the original constructor before
        # deprecation wrapping if any
        init = getattr(cls.__init__, "deprecated_original", cls.__init__)
        if init is object.__init__:
            # No explicit constructor to introspect
            return []

        # introspect the constructor arguments to find the model parameters
        # to represent
        init_signature = inspect.signature(init)
        # Consider the constructor parameters excluding 'self'
        parameters = [
            p
            for p in init_signature.parameters.values()
            if p.name != "self" and p.kind != p.VAR_KEYWORD
        ]
        for p in parameters:
            if p.kind == p.VAR_POSITIONAL:
                raise RuntimeError(
                    "scikit-learn estimators should always "
                    "specify their parameters in the signature"
                    " of their __init__ (no varargs)."
                    " %s with constructor %s doesn't "
                    " follow this convention." % (cls, init_signature)
                )
        # Extract and sort argument names excluding 'self'
        return sorted([p.name for p in parameters])

    def get_params(self, deep=True):
        """
        Get parameters for this estimator.

        Parameters
        ----------
        deep : bool, default=True
            If True, will return the parameters for this estimator and
            contained subobjects that are estimators.

        Returns
        -------
        params : dict
            Parameter names mapped to their values.
        """
        out = dict()
        for key in self._get_param_names():
            value = getattr(self, key)
            if deep and hasattr(value, "get_params") and not isinstance(value, type):
                deep_items = value.get_params().items()
                out.update((key + "__" + k, val) for k, val in deep_items)
            out[key] = value
        return out

    def set_params(self, **params):
        """Set the parameters of this estimator.

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

        Parameters
        ----------
        **params : dict
            Estimator parameters.

        Returns
        -------
        self : estimator instance
            Estimator instance.
        """
        if not params:
            # Simple optimization to gain speed (inspect is slow)
            return self
        valid_params = self.get_params(deep=True)

        nested_params = defaultdict(dict)  # grouped by prefix
        for key, value in params.items():
            key, delim, sub_key = key.partition("__")
            if key not in valid_params:
                local_valid_params = self._get_param_names()
                raise ValueError(
                    f"Invalid parameter {key!r} for estimator {self}. "
                    f"Valid parameters are: {local_valid_params!r}."
                )

            if delim:
                nested_params[key][sub_key] = value
            else:
                setattr(self, key, value)
                valid_params[key] = value

        for key, sub_params in nested_params.items():
            # TODO(1.4): remove specific handling of "base_estimator".
            # The "base_estimator" key is special. It was deprecated and
            # renamed to "estimator" for several estimators. This means we
            # need to translate it here and set sub-parameters on "estimator",
            # but only if the user did not explicitly set a value for
            # "base_estimator".
            if (
                key == "base_estimator"
                and valid_params[key] == "deprecated"
                and self.__module__.startswith("sklearn.")
            ):
                warnings.warn(
                    f"Parameter 'base_estimator' of {self.__class__.__name__} is"
                    " deprecated in favor of 'estimator'. See"
                    f" {self.__class__.__name__}'s docstring for more details.",
                    FutureWarning,
                    stacklevel=2,
                )
                key = "estimator"
            valid_params[key].set_params(**sub_params)

        return self

    def __repr__(self, N_CHAR_MAX=700):
        # N_CHAR_MAX is the (approximate) maximum number of non-blank
        # characters to render. We pass it as an optional parameter to ease
        # the tests.

        from .utils._pprint import _EstimatorPrettyPrinter

        N_MAX_ELEMENTS_TO_SHOW = 30  # number of elements to show in sequences

        # use ellipsis for sequences with a lot of elements
        pp = _EstimatorPrettyPrinter(
            compact=True,
            indent=1,
            indent_at_name=True,
            n_max_elements_to_show=N_MAX_ELEMENTS_TO_SHOW,
        )

        repr_ = pp.pformat(self)

        # Use bruteforce ellipsis when there are a lot of non-blank characters
        n_nonblank = len("".join(repr_.split()))
        if n_nonblank > N_CHAR_MAX:
            lim = N_CHAR_MAX // 2  # apprx number of chars to keep on both ends
            regex = r"^(\s*\S){%d}" % lim
            # The regex '^(\s*\S){%d}' % n
            # matches from the start of the string until the nth non-blank
            # character:
            # - ^ matches the start of string
            # - (pattern){n} matches n repetitions of pattern
            # - \s*\S matches a non-blank char following zero or more blanks
            left_lim = re.match(regex, repr_).end()
            right_lim = re.match(regex, repr_[::-1]).end()

            if "\n" in repr_[left_lim:-right_lim]:
                # The left side and right side aren't on the same line.
                # To avoid weird cuts, e.g.:
                # categoric...ore',
                # we need to start the right side with an appropriate newline
                # character so that it renders properly as:
                # categoric...
                # handle_unknown='ignore',
                # so we add [^\n]*\n which matches until the next \n
                regex += r"[^\n]*\n"
                right_lim = re.match(regex, repr_[::-1]).end()

            ellipsis = "..."
            if left_lim + len(ellipsis) < len(repr_) - right_lim:
                # Only add ellipsis if it results in a shorter repr
                repr_ = repr_[:left_lim] + "..." + repr_[-right_lim:]

        return repr_

    def __getstate__(self):
        if getattr(self, "__slots__", None):
            raise TypeError(
                "You cannot use `__slots__` in objects inheriting from "
                "`sklearn.base.BaseEstimator`."
            )

        try:
            state = super().__getstate__()
            if state is None:
                # For Python 3.11+, empty instance (no `__slots__`,
                # and `__dict__`) will return a state equal to `None`.
                state = self.__dict__.copy()
        except AttributeError:
            # Python < 3.11
            state = self.__dict__.copy()

        if type(self).__module__.startswith("sklearn."):
            return dict(state.items(), _sklearn_version=__version__)
        else:
            return state

    def __setstate__(self, state):
        if type(self).__module__.startswith("sklearn."):
            pickle_version = state.pop("_sklearn_version", "pre-0.18")
            if pickle_version != __version__:
                warnings.warn(
                    "Trying to unpickle estimator {0} from version {1} when "
                    "using version {2}. This might lead to breaking code or "
                    "invalid results. Use at your own risk. "
                    "For more info please refer to:\n"
                    "https://scikit-learn.org/stable/model_persistence.html"
                    "#security-maintainability-limitations".format(
                        self.__class__.__name__, pickle_version, __version__
                    ),
                    UserWarning,
                )
        try:
            super().__setstate__(state)
        except AttributeError:
            self.__dict__.update(state)

    def _more_tags(self):
        return _DEFAULT_TAGS

    def _get_tags(self):
        collected_tags = {}
        for base_class in reversed(inspect.getmro(self.__class__)):
            if hasattr(base_class, "_more_tags"):
                # need the if because mixins might not have _more_tags
                # but might do redundant work in estimators
                # (i.e. calling more tags on BaseEstimator multiple times)
                more_tags = base_class._more_tags(self)
                collected_tags.update(more_tags)
        return collected_tags

    def _check_n_features(self, X, reset):
        """Set the `n_features_in_` attribute, or check against it.

        Parameters
        ----------
        X : {ndarray, sparse matrix} of shape (n_samples, n_features)
            The input samples.
        reset : bool
            If True, the `n_features_in_` attribute is set to `X.shape[1]`.
            If False and the attribute exists, then check that it is equal to
            `X.shape[1]`. If False and the attribute does *not* exist, then
            the check is skipped.
            .. note::
               It is recommended to call reset=True in `fit` and in the first
               call to `partial_fit`. All other methods that validate `X`
               should set `reset=False`.
        """
        try:
            n_features = _num_features(X)
        except TypeError as e:
            if not reset and hasattr(self, "n_features_in_"):
                raise ValueError(
                    "X does not contain any features, but "
                    f"{self.__class__.__name__} is expecting "
                    f"{self.n_features_in_} features"
                ) from e
            # If the number of features is not defined and reset=True,
            # then we skip this check
            return

        if reset:
            self.n_features_in_ = n_features
            return

        if not hasattr(self, "n_features_in_"):
            # Skip this check if the expected number of expected input features
            # was not recorded by calling fit first. This is typically the case
            # for stateless transformers.
            return

        if n_features != self.n_features_in_:
            raise ValueError(
                f"X has {n_features} features, but {self.__class__.__name__} "
                f"is expecting {self.n_features_in_} features as input."
            )

    def _check_feature_names(self, X, *, reset):
        """Set or check the `feature_names_in_` attribute.

        .. versionadded:: 1.0

        Parameters
        ----------
        X : {ndarray, dataframe} of shape (n_samples, n_features)
            The input samples.

        reset : bool
            Whether to reset the `feature_names_in_` attribute.
            If False, the input will be checked for consistency with
            feature names of data provided when reset was last True.
            .. note::
               It is recommended to call `reset=True` in `fit` and in the first
               call to `partial_fit`. All other methods that validate `X`
               should set `reset=False`.
        """

        if reset:
            feature_names_in = _get_feature_names(X)
            if feature_names_in is not None:
                self.feature_names_in_ = feature_names_in
            elif hasattr(self, "feature_names_in_"):
                # Delete the attribute when the estimator is fitted on a new dataset
                # that has no feature names.
                delattr(self, "feature_names_in_")
            return

        fitted_feature_names = getattr(self, "feature_names_in_", None)
        X_feature_names = _get_feature_names(X)

        if fitted_feature_names is None and X_feature_names is None:
            # no feature names seen in fit and in X
            return

        if X_feature_names is not None and fitted_feature_names is None:
            warnings.warn(
                f"X has feature names, but {self.__class__.__name__} was fitted without"
                " feature names"
            )
            return

        if X_feature_names is None and fitted_feature_names is not None:
            warnings.warn(
                "X does not have valid feature names, but"
                f" {self.__class__.__name__} was fitted with feature names"
            )
            return

        # validate the feature names against the `feature_names_in_` attribute
        if len(fitted_feature_names) != len(X_feature_names) or np.any(
            fitted_feature_names != X_feature_names
        ):
            message = (
                "The feature names should match those that were passed during fit.\n"
            )
            fitted_feature_names_set = set(fitted_feature_names)
            X_feature_names_set = set(X_feature_names)

            unexpected_names = sorted(X_feature_names_set - fitted_feature_names_set)
            missing_names = sorted(fitted_feature_names_set - X_feature_names_set)

            def add_names(names):
                output = ""
                max_n_names = 5
                for i, name in enumerate(names):
                    if i >= max_n_names:
                        output += "- ...\n"
                        break
                    output += f"- {name}\n"
                return output

            if unexpected_names:
                message += "Feature names unseen at fit time:\n"
                message += add_names(unexpected_names)

            if missing_names:
                message += "Feature names seen at fit time, yet now missing:\n"
                message += add_names(missing_names)

            if not missing_names and not unexpected_names:
                message += (
                    "Feature names must be in the same order as they were in fit.\n"
                )

            raise ValueError(message)

    def _validate_data(
        self,
        X="no_validation",
        y="no_validation",
        reset=True,
        validate_separately=False,
        **check_params,
    ):
        """Validate input data and set or check the `n_features_in_` attribute.

        Parameters
        ----------
        X : {array-like, sparse matrix, dataframe} of shape \
                (n_samples, n_features), default='no validation'
            The input samples.
            If `'no_validation'`, no validation is performed on `X`. This is
            useful for meta-estimator which can delegate input validation to
            their underlying estimator(s). In that case `y` must be passed and
            the only accepted `check_params` are `multi_output` and
            `y_numeric`.

        y : array-like of shape (n_samples,), default='no_validation'
            The targets.

            - If `None`, `check_array` is called on `X`. If the estimator's
              requires_y tag is True, then an error will be raised.
            - If `'no_validation'`, `check_array` is called on `X` and the
              estimator's requires_y tag is ignored. This is a default
              placeholder and is never meant to be explicitly set. In that case
              `X` must be passed.
            - Otherwise, only `y` with `_check_y` or both `X` and `y` are
              checked with either `check_array` or `check_X_y` depending on
              `validate_separately`.

        reset : bool, default=True
            Whether to reset the `n_features_in_` attribute.
            If False, the input will be checked for consistency with data
            provided when reset was last True.
            .. note::
               It is recommended to call reset=True in `fit` and in the first
               call to `partial_fit`. All other methods that validate `X`
               should set `reset=False`.

        validate_separately : False or tuple of dicts, default=False
            Only used if y is not None.
            If False, call validate_X_y(). Else, it must be a tuple of kwargs
            to be used for calling check_array() on X and y respectively.

            `estimator=self` is automatically added to these dicts to generate
            more informative error message in case of invalid input data.

        **check_params : kwargs
            Parameters passed to :func:`sklearn.utils.check_array` or
            :func:`sklearn.utils.check_X_y`. Ignored if validate_separately
            is not False.

            `estimator=self` is automatically added to these params to generate
            more informative error message in case of invalid input data.

        Returns
        -------
        out : {ndarray, sparse matrix} or tuple of these
            The validated input. A tuple is returned if both `X` and `y` are
            validated.
        """
        self._check_feature_names(X, reset=reset)

        if y is None and self._get_tags()["requires_y"]:
            raise ValueError(
                f"This {self.__class__.__name__} estimator "
                "requires y to be passed, but the target y is None."
            )

        no_val_X = isinstance(X, str) and X == "no_validation"
        no_val_y = y is None or isinstance(y, str) and y == "no_validation"

        default_check_params = {"estimator": self}
        check_params = {**default_check_params, **check_params}

        if no_val_X and no_val_y:
            raise ValueError("Validation should be done on X, y or both.")
        elif not no_val_X and no_val_y:
            X = check_array(X, input_name="X", **check_params)
            out = X
        elif no_val_X and not no_val_y:
            y = _check_y(y, **check_params)
            out = y
        else:
            if validate_separately:
                # We need this because some estimators validate X and y
                # separately, and in general, separately calling check_array()
                # on X and y isn't equivalent to just calling check_X_y()
                # :(
                check_X_params, check_y_params = validate_separately
                if "estimator" not in check_X_params:
                    check_X_params = {**default_check_params, **check_X_params}
                X = check_array(X, input_name="X", **check_X_params)
                if "estimator" not in check_y_params:
                    check_y_params = {**default_check_params, **check_y_params}
                y = check_array(y, input_name="y", **check_y_params)
            else:
                X, y = check_X_y(X, y, **check_params)
            out = X, y

        if not no_val_X and check_params.get("ensure_2d", True):
            self._check_n_features(X, reset=reset)

        return out

    def _validate_params(self):
        """Validate types and values of constructor parameters

        The expected type and values must be defined in the `_parameter_constraints`
        class attribute, which is a dictionary `param_name: list of constraints`. See
        the docstring of `validate_parameter_constraints` for a description of the
        accepted constraints.
        """
        validate_parameter_constraints(
            self._parameter_constraints,
            self.get_params(deep=False),
            caller_name=self.__class__.__name__,
        )

    @property
    def _repr_html_(self):
        """HTML representation of estimator.

        This is redundant with the logic of `_repr_mimebundle_`. The latter
        should be favorted in the long term, `_repr_html_` is only
        implemented for consumers who do not interpret `_repr_mimbundle_`.
        """
        if get_config()["display"] != "diagram":
            raise AttributeError(
                "_repr_html_ is only defined when the "
                "'display' configuration option is set to "
                "'diagram'"
            )
        return self._repr_html_inner

    def _repr_html_inner(self):
        """This function is returned by the @property `_repr_html_` to make
        `hasattr(estimator, "_repr_html_") return `True` or `False` depending
        on `get_config()["display"]`.
        """
        return estimator_html_repr(self)

    def _repr_mimebundle_(self, **kwargs):
        """Mime bundle used by jupyter kernels to display estimator"""
        output = {"text/plain": repr(self)}
        if get_config()["display"] == "diagram":
            output["text/html"] = estimator_html_repr(self)
        return output


class ClassifierMixin:
    """Mixin class for all classifiers in scikit-learn."""

    _estimator_type = "classifier"

    def score(self, X, y, sample_weight=None):
        """
        Return the mean accuracy on the given test data and labels.

        In multi-label classification, this is the subset accuracy
        which is a harsh metric since you require for each sample that
        each label set be correctly predicted.

        Parameters
        ----------
        X : array-like of shape (n_samples, n_features)
            Test samples.

        y : array-like of shape (n_samples,) or (n_samples, n_outputs)
            True labels for `X`.

        sample_weight : array-like of shape (n_samples,), default=None
            Sample weights.

        Returns
        -------
        score : float
            Mean accuracy of ``self.predict(X)`` w.r.t. `y`.
        """
        from .metrics import accuracy_score

        return accuracy_score(y, self.predict(X), sample_weight=sample_weight)

    def _more_tags(self):
        return {"requires_y": True}


class RegressorMixin:
    """Mixin class for all regression estimators in scikit-learn."""

    _estimator_type = "regressor"

    def score(self, X, y, sample_weight=None):
        """Return the coefficient of determination of the prediction.

        The coefficient of determination :math:`R^2` is defined as
        :math:`(1 - \\frac{u}{v})`, where :math:`u` is the residual
        sum of squares ``((y_true - y_pred)** 2).sum()`` and :math:`v`
        is the total sum of squares ``((y_true - y_true.mean()) ** 2).sum()``.
        The best possible score is 1.0 and it can be negative (because the
        model can be arbitrarily worse). A constant model that always predicts
        the expected value of `y`, disregarding the input features, would get
        a :math:`R^2` score of 0.0.

        Parameters
        ----------
        X : array-like of shape (n_samples, n_features)
            Test samples. For some estimators this may be a precomputed
            kernel matrix or a list of generic objects instead with shape
            ``(n_samples, n_samples_fitted)``, where ``n_samples_fitted``
            is the number of samples used in the fitting for the estimator.

        y : array-like of shape (n_samples,) or (n_samples, n_outputs)
            True values for `X`.

        sample_weight : array-like of shape (n_samples,), default=None
            Sample weights.

        Returns
        -------
        score : float
            :math:`R^2` of ``self.predict(X)`` w.r.t. `y`.

        Notes
        -----
        The :math:`R^2` score used when calling ``score`` on a regressor uses
        ``multioutput='uniform_average'`` from version 0.23 to keep consistent
        with default value of :func:`~sklearn.metrics.r2_score`.
        This influences the ``score`` method of all the multioutput
        regressors (except for
        :class:`~sklearn.multioutput.MultiOutputRegressor`).
        """

        from .metrics import r2_score

        y_pred = self.predict(X)
        return r2_score(y, y_pred, sample_weight=sample_weight)

    def _more_tags(self):
        return {"requires_y": True}


class ClusterMixin:
    """Mixin class for all cluster estimators in scikit-learn."""

    _estimator_type = "clusterer"

    def fit_predict(self, X, y=None):
        """
        Perform clustering on `X` and returns cluster labels.

        Parameters
        ----------
        X : array-like of shape (n_samples, n_features)
            Input data.

        y : Ignored
            Not used, present for API consistency by convention.

        Returns
        -------
        labels : ndarray of shape (n_samples,), dtype=np.int64
            Cluster labels.
        """
        # non-optimized default implementation; override when a better
        # method is possible for a given clustering algorithm
        self.fit(X)
        return self.labels_

    def _more_tags(self):
        return {"preserves_dtype": []}


class BiclusterMixin:
    """Mixin class for all bicluster estimators in scikit-learn."""

    @property
    def biclusters_(self):
        """Convenient way to get row and column indicators together.

        Returns the ``rows_`` and ``columns_`` members.
        """
        return self.rows_, self.columns_

    def get_indices(self, i):
        """Row and column indices of the `i`'th bicluster.

        Only works if ``rows_`` and ``columns_`` attributes exist.

        Parameters
        ----------
        i : int
            The index of the cluster.

        Returns
        -------
        row_ind : ndarray, dtype=np.intp
            Indices of rows in the dataset that belong to the bicluster.
        col_ind : ndarray, dtype=np.intp
            Indices of columns in the dataset that belong to the bicluster.
        """
        rows = self.rows_[i]
        columns = self.columns_[i]
        return np.nonzero(rows)[0], np.nonzero(columns)[0]

    def get_shape(self, i):
        """Shape of the `i`'th bicluster.

        Parameters
        ----------
        i : int
            The index of the cluster.

        Returns
        -------
        n_rows : int
            Number of rows in the bicluster.

        n_cols : int
            Number of columns in the bicluster.
        """
        indices = self.get_indices(i)
        return tuple(len(i) for i in indices)

    def get_submatrix(self, i, data):
        """Return the submatrix corresponding to bicluster `i`.

        Parameters
        ----------
        i : int
            The index of the cluster.
        data : array-like of shape (n_samples, n_features)
            The data.

        Returns
        -------
        submatrix : ndarray of shape (n_rows, n_cols)
            The submatrix corresponding to bicluster `i`.

        Notes
        -----
        Works with sparse matrices. Only works if ``rows_`` and
        ``columns_`` attributes exist.
        """
        from .utils.validation import check_array

        data = check_array(data, accept_sparse="csr")
        row_ind, col_ind = self.get_indices(i)
        return data[row_ind[:, np.newaxis], col_ind]


class TransformerMixin(_SetOutputMixin):
    """Mixin class for all transformers in scikit-learn.

    If :term:`get_feature_names_out` is defined, then `BaseEstimator` will
    automatically wrap `transform` and `fit_transform` to follow the `set_output`
    API. See the :ref:`developer_api_set_output` for details.

    :class:`base.OneToOneFeatureMixin` and
    :class:`base.ClassNamePrefixFeaturesOutMixin` are helpful mixins for
    defining :term:`get_feature_names_out`.
    """

    def fit_transform(self, X, y=None, **fit_params):
        """
        Fit to data, then transform it.

        Fits transformer to `X` and `y` with optional parameters `fit_params`
        and returns a transformed version of `X`.

        Parameters
        ----------
        X : array-like of shape (n_samples, n_features)
            Input samples.

        y :  array-like of shape (n_samples,) or (n_samples, n_outputs), \
                default=None
            Target values (None for unsupervised transformations).

        **fit_params : dict
            Additional fit parameters.

        Returns
        -------
        X_new : ndarray array of shape (n_samples, n_features_new)
            Transformed array.
        """
        # non-optimized default implementation; override when a better
        # method is possible for a given clustering algorithm
        if y is None:
            # fit method of arity 1 (unsupervised transformation)
            return self.fit(X, **fit_params).transform(X)
        else:
            # fit method of arity 2 (supervised transformation)
            return self.fit(X, y, **fit_params).transform(X)


class OneToOneFeatureMixin:
    """Provides `get_feature_names_out` for simple transformers.

    This mixin assumes there's a 1-to-1 correspondence between input features
    and output features, such as :class:`~preprocessing.StandardScaler`.
    """

    def get_feature_names_out(self, input_features=None):
        """Get output feature names for transformation.

        Parameters
        ----------
        input_features : array-like of str or None, default=None
            Input features.

            - If `input_features` is `None`, then `feature_names_in_` is
              used as feature names in. If `feature_names_in_` is not defined,
              then the following input feature names are generated:
              `["x0", "x1", ..., "x(n_features_in_ - 1)"]`.
            - If `input_features` is an array-like, then `input_features` must
              match `feature_names_in_` if `feature_names_in_` is defined.

        Returns
        -------
        feature_names_out : ndarray of str objects
            Same as input features.
        """
        return _check_feature_names_in(self, input_features)


class ClassNamePrefixFeaturesOutMixin:
    """Mixin class for transformers that generate their own names by prefixing.

    This mixin is useful when the transformer needs to generate its own feature
    names out, such as :class:`~decomposition.PCA`. For example, if
    :class:`~decomposition.PCA` outputs 3 features, then the generated feature
    names out are: `["pca0", "pca1", "pca2"]`.

    This mixin assumes that a `_n_features_out` attribute is defined when the
    transformer is fitted. `_n_features_out` is the number of output features
    that the transformer will return in `transform` of `fit_transform`.
    """

    def get_feature_names_out(self, input_features=None):
        """Get output feature names for transformation.

        The feature names out will prefixed by the lowercased class name. For
        example, if the transformer outputs 3 features, then the feature names
        out are: `["class_name0", "class_name1", "class_name2"]`.

        Parameters
        ----------
        input_features : array-like of str or None, default=None
            Only used to validate feature names with the names seen in :meth:`fit`.

        Returns
        -------
        feature_names_out : ndarray of str objects
            Transformed feature names.
        """
        check_is_fitted(self, "_n_features_out")
        return _generate_get_feature_names_out(
            self, self._n_features_out, input_features=input_features
        )


class DensityMixin:
    """Mixin class for all density estimators in scikit-learn."""

    _estimator_type = "DensityEstimator"

    def score(self, X, y=None):
        """Return the score of the model on the data `X`.

        Parameters
        ----------
        X : array-like of shape (n_samples, n_features)
            Test samples.

        y : Ignored
            Not used, present for API consistency by convention.

        Returns
        -------
        score : float
        """
        pass


class OutlierMixin:
    """Mixin class for all outlier detection estimators in scikit-learn."""

    _estimator_type = "outlier_detector"

    def fit_predict(self, X, y=None):
        """Perform fit on X and returns labels for X.

        Returns -1 for outliers and 1 for inliers.

        Parameters
        ----------
        X : {array-like, sparse matrix} of shape (n_samples, n_features)
            The input samples.

        y : Ignored
            Not used, present for API consistency by convention.

        Returns
        -------
        y : ndarray of shape (n_samples,)
            1 for inliers, -1 for outliers.
        """
        # override for transductive outlier detectors like LocalOulierFactor
        return self.fit(X).predict(X)


class MetaEstimatorMixin:
    _required_parameters = ["estimator"]
    """Mixin class for all meta estimators in scikit-learn."""


class MultiOutputMixin:
    """Mixin to mark estimators that support multioutput."""

    def _more_tags(self):
        return {"multioutput": True}


class _UnstableArchMixin:
    """Mark estimators that are non-determinstic on 32bit or PowerPC"""

    def _more_tags(self):
        return {
            "non_deterministic": (
                _IS_32BIT or platform.machine().startswith(("ppc", "powerpc"))
            )
        }


def is_classifier(estimator):
    """Return True if the given estimator is (probably) a classifier.

    Parameters
    ----------
    estimator : object
        Estimator object to test.

    Returns
    -------
    out : bool
        True if estimator is a classifier and False otherwise.
    """
    return getattr(estimator, "_estimator_type", None) == "classifier"


def is_regressor(estimator):
    """Return True if the given estimator is (probably) a regressor.

    Parameters
    ----------
    estimator : estimator instance
        Estimator object to test.

    Returns
    -------
    out : bool
        True if estimator is a regressor and False otherwise.
    """
    return getattr(estimator, "_estimator_type", None) == "regressor"


def is_outlier_detector(estimator):
    """Return True if the given estimator is (probably) an outlier detector.

    Parameters
    ----------
    estimator : estimator instance
        Estimator object to test.

    Returns
    -------
    out : bool
        True if estimator is an outlier detector and False otherwise.
    """
    return getattr(estimator, "_estimator_type", None) == "outlier_detector"