"""Nearest Neighbor Classification""" # Authors: Jake Vanderplas # Fabian Pedregosa # Alexandre Gramfort # Sparseness support by Lars Buitinck # Multi-output support by Arnaud Joly # # License: BSD 3 clause (C) INRIA, University of Amsterdam import numpy as np from scipy import stats from ..utils.extmath import weighted_mode from .base import \ _check_weights, _get_weights, \ NeighborsBase, KNeighborsMixin,\ RadiusNeighborsMixin, SupervisedIntegerMixin from ..base import ClassifierMixin from ..utils import check_array class KNeighborsClassifier(NeighborsBase, KNeighborsMixin, SupervisedIntegerMixin, ClassifierMixin): """Classifier implementing the k-nearest neighbors vote. Read more in the :ref:`User Guide `. Parameters ---------- n_neighbors : int, optional (default = 5) Number of neighbors to use by default for :meth:`kneighbors` queries. weights : str or callable, optional (default = 'uniform') weight function used in prediction. Possible values: - 'uniform' : uniform weights. All points in each neighborhood are weighted equally. - 'distance' : weight points by the inverse of their distance. in this case, closer neighbors of a query point will have a greater influence than neighbors which are further away. - [callable] : a user-defined function which accepts an array of distances, and returns an array of the same shape containing the weights. algorithm : {'auto', 'ball_tree', 'kd_tree', 'brute'}, optional Algorithm used to compute the nearest neighbors: - 'ball_tree' will use :class:`BallTree` - 'kd_tree' will use :class:`KDTree` - 'brute' will use a brute-force search. - 'auto' will attempt to decide the most appropriate algorithm based on the values passed to :meth:`fit` method. Note: fitting on sparse input will override the setting of this parameter, using brute force. leaf_size : int, optional (default = 30) Leaf size passed to BallTree or KDTree. This can affect the speed of the construction and query, as well as the memory required to store the tree. The optimal value depends on the nature of the problem. p : integer, optional (default = 2) Power parameter for the Minkowski metric. When p = 1, this is equivalent to using manhattan_distance (l1), and euclidean_distance (l2) for p = 2. For arbitrary p, minkowski_distance (l_p) is used. metric : string or callable, default 'minkowski' the distance metric to use for the tree. The default metric is minkowski, and with p=2 is equivalent to the standard Euclidean metric. See the documentation of the DistanceMetric class for a list of available metrics. metric_params : dict, optional (default = None) Additional keyword arguments for the metric function. n_jobs : int or None, optional (default=None) The number of parallel jobs to run for neighbors search. ``None`` means 1 unless in a :obj:`joblib.parallel_backend` context. ``-1`` means using all processors. See :term:`Glossary ` for more details. Doesn't affect :meth:`fit` method. Examples -------- >>> X = [[0], [1], [2], [3]] >>> y = [0, 0, 1, 1] >>> from sklearn.neighbors import KNeighborsClassifier >>> neigh = KNeighborsClassifier(n_neighbors=3) >>> neigh.fit(X, y) # doctest: +ELLIPSIS KNeighborsClassifier(...) >>> print(neigh.predict([[1.1]])) [0] >>> print(neigh.predict_proba([[0.9]])) [[0.66666667 0.33333333]] See also -------- RadiusNeighborsClassifier KNeighborsRegressor RadiusNeighborsRegressor NearestNeighbors Notes ----- See :ref:`Nearest Neighbors ` in the online documentation for a discussion of the choice of ``algorithm`` and ``leaf_size``. .. warning:: Regarding the Nearest Neighbors algorithms, if it is found that two neighbors, neighbor `k+1` and `k`, have identical distances but different labels, the results will depend on the ordering of the training data. https://en.wikipedia.org/wiki/K-nearest_neighbor_algorithm """ def __init__(self, n_neighbors=5, weights='uniform', algorithm='auto', leaf_size=30, p=2, metric='minkowski', metric_params=None, n_jobs=None, **kwargs): super(KNeighborsClassifier, self).__init__( n_neighbors=n_neighbors, algorithm=algorithm, leaf_size=leaf_size, metric=metric, p=p, metric_params=metric_params, n_jobs=n_jobs, **kwargs) self.weights = _check_weights(weights) def predict(self, X): """Predict the class labels for the provided data Parameters ---------- X : array-like, shape (n_query, n_features), \ or (n_query, n_indexed) if metric == 'precomputed' Test samples. Returns ------- y : array of shape [n_samples] or [n_samples, n_outputs] Class labels for each data sample. """ X = check_array(X, accept_sparse='csr') neigh_dist, neigh_ind = self.kneighbors(X) classes_ = self.classes_ _y = self._y if not self.outputs_2d_: _y = self._y.reshape((-1, 1)) classes_ = [self.classes_] n_outputs = len(classes_) n_samples = X.shape[0] weights = _get_weights(neigh_dist, self.weights) y_pred = np.empty((n_samples, n_outputs), dtype=classes_[0].dtype) for k, classes_k in enumerate(classes_): if weights is None: mode, _ = stats.mode(_y[neigh_ind, k], axis=1) else: mode, _ = weighted_mode(_y[neigh_ind, k], weights, axis=1) mode = np.asarray(mode.ravel(), dtype=np.intp) y_pred[:, k] = classes_k.take(mode) if not self.outputs_2d_: y_pred = y_pred.ravel() return y_pred def predict_proba(self, X): """Return probability estimates for the test data X. Parameters ---------- X : array-like, shape (n_query, n_features), \ or (n_query, n_indexed) if metric == 'precomputed' Test samples. Returns ------- p : array of shape = [n_samples, n_classes], or a list of n_outputs of such arrays if n_outputs > 1. The class probabilities of the input samples. Classes are ordered by lexicographic order. """ X = check_array(X, accept_sparse='csr') neigh_dist, neigh_ind = self.kneighbors(X) classes_ = self.classes_ _y = self._y if not self.outputs_2d_: _y = self._y.reshape((-1, 1)) classes_ = [self.classes_] n_samples = X.shape[0] weights = _get_weights(neigh_dist, self.weights) if weights is None: weights = np.ones_like(neigh_ind) all_rows = np.arange(X.shape[0]) probabilities = [] for k, classes_k in enumerate(classes_): pred_labels = _y[:, k][neigh_ind] proba_k = np.zeros((n_samples, classes_k.size)) # a simple ':' index doesn't work right for i, idx in enumerate(pred_labels.T): # loop is O(n_neighbors) proba_k[all_rows, idx] += weights[:, i] # normalize 'votes' into real [0,1] probabilities normalizer = proba_k.sum(axis=1)[:, np.newaxis] normalizer[normalizer == 0.0] = 1.0 proba_k /= normalizer probabilities.append(proba_k) if not self.outputs_2d_: probabilities = probabilities[0] return probabilities class RadiusNeighborsClassifier(NeighborsBase, RadiusNeighborsMixin, SupervisedIntegerMixin, ClassifierMixin): """Classifier implementing a vote among neighbors within a given radius Read more in the :ref:`User Guide `. Parameters ---------- radius : float, optional (default = 1.0) Range of parameter space to use by default for :meth:`radius_neighbors` queries. weights : str or callable weight function used in prediction. Possible values: - 'uniform' : uniform weights. All points in each neighborhood are weighted equally. - 'distance' : weight points by the inverse of their distance. in this case, closer neighbors of a query point will have a greater influence than neighbors which are further away. - [callable] : a user-defined function which accepts an array of distances, and returns an array of the same shape containing the weights. Uniform weights are used by default. algorithm : {'auto', 'ball_tree', 'kd_tree', 'brute'}, optional Algorithm used to compute the nearest neighbors: - 'ball_tree' will use :class:`BallTree` - 'kd_tree' will use :class:`KDTree` - 'brute' will use a brute-force search. - 'auto' will attempt to decide the most appropriate algorithm based on the values passed to :meth:`fit` method. Note: fitting on sparse input will override the setting of this parameter, using brute force. leaf_size : int, optional (default = 30) Leaf size passed to BallTree or KDTree. This can affect the speed of the construction and query, as well as the memory required to store the tree. The optimal value depends on the nature of the problem. p : integer, optional (default = 2) Power parameter for the Minkowski metric. When p = 1, this is equivalent to using manhattan_distance (l1), and euclidean_distance (l2) for p = 2. For arbitrary p, minkowski_distance (l_p) is used. metric : string or callable, default 'minkowski' the distance metric to use for the tree. The default metric is minkowski, and with p=2 is equivalent to the standard Euclidean metric. See the documentation of the DistanceMetric class for a list of available metrics. outlier_label : int, optional (default = None) Label, which is given for outlier samples (samples with no neighbors on given radius). If set to None, ValueError is raised, when outlier is detected. metric_params : dict, optional (default = None) Additional keyword arguments for the metric function. n_jobs : int or None, optional (default=None) The number of parallel jobs to run for neighbors search. ``None`` means 1 unless in a :obj:`joblib.parallel_backend` context. ``-1`` means using all processors. See :term:`Glossary ` for more details. Examples -------- >>> X = [[0], [1], [2], [3]] >>> y = [0, 0, 1, 1] >>> from sklearn.neighbors import RadiusNeighborsClassifier >>> neigh = RadiusNeighborsClassifier(radius=1.0) >>> neigh.fit(X, y) # doctest: +ELLIPSIS RadiusNeighborsClassifier(...) >>> print(neigh.predict([[1.5]])) [0] See also -------- KNeighborsClassifier RadiusNeighborsRegressor KNeighborsRegressor NearestNeighbors Notes ----- See :ref:`Nearest Neighbors ` in the online documentation for a discussion of the choice of ``algorithm`` and ``leaf_size``. https://en.wikipedia.org/wiki/K-nearest_neighbor_algorithm """ def __init__(self, radius=1.0, weights='uniform', algorithm='auto', leaf_size=30, p=2, metric='minkowski', outlier_label=None, metric_params=None, n_jobs=None, **kwargs): super(RadiusNeighborsClassifier, self).__init__( radius=radius, algorithm=algorithm, leaf_size=leaf_size, metric=metric, p=p, metric_params=metric_params, n_jobs=n_jobs, **kwargs) self.weights = _check_weights(weights) self.outlier_label = outlier_label def predict(self, X): """Predict the class labels for the provided data Parameters ---------- X : array-like, shape (n_query, n_features), \ or (n_query, n_indexed) if metric == 'precomputed' Test samples. Returns ------- y : array of shape [n_samples] or [n_samples, n_outputs] Class labels for each data sample. """ X = check_array(X, accept_sparse='csr') n_samples = X.shape[0] neigh_dist, neigh_ind = self.radius_neighbors(X) inliers = [i for i, nind in enumerate(neigh_ind) if len(nind) != 0] outliers = [i for i, nind in enumerate(neigh_ind) if len(nind) == 0] classes_ = self.classes_ _y = self._y if not self.outputs_2d_: _y = self._y.reshape((-1, 1)) classes_ = [self.classes_] n_outputs = len(classes_) if self.outlier_label is not None: neigh_dist[outliers] = 1e-6 elif outliers: raise ValueError('No neighbors found for test samples %r, ' 'you can try using larger radius, ' 'give a label for outliers, ' 'or consider removing them from your dataset.' % outliers) weights = _get_weights(neigh_dist, self.weights) y_pred = np.empty((n_samples, n_outputs), dtype=classes_[0].dtype) for k, classes_k in enumerate(classes_): pred_labels = np.zeros(len(neigh_ind), dtype=object) pred_labels[:] = [_y[ind, k] for ind in neigh_ind] if weights is None: mode = np.array([stats.mode(pl)[0] for pl in pred_labels[inliers]], dtype=np.int) else: mode = np.array( [weighted_mode(pl, w)[0] for (pl, w) in zip(pred_labels[inliers], weights[inliers]) ], dtype=np.int) mode = mode.ravel() y_pred[inliers, k] = classes_k.take(mode) if outliers: y_pred[outliers, :] = self.outlier_label if not self.outputs_2d_: y_pred = y_pred.ravel() return y_pred