skhubness.neighbors.KNeighborsClassifier¶

class skhubness.neighbors.KNeighborsClassifier(n_neighbors: int = 5, weights: str = 'uniform', algorithm: str = 'auto', algorithm_params: dict = None, hubness: str = None, hubness_params: dict = None, leaf_size: int = 30, p=2, metric='minkowski', metric_params=None, n_jobs=None, verbose: int = 0, **kwargs)[source]¶

Classifier implementing the k-nearest neighbors vote.

Read more in the scikit-learn User Guide

Parameters

n_neighbors: int, optional (default = 5)

Number of neighbors to use by default for 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’, ‘hnsw’, ‘lsh’, ‘falconn_lsh’, ‘nng’, ‘rptree’, ‘ball_tree’, ‘kd_tree’, ‘brute’}, optional

Algorithm used to compute the nearest neighbors:

‘hnsw’ will use HNSW
‘lsh’ will use PuffinnLSH
‘falconn_lsh’ will use FalconnLSH
‘nng’ will use NNG
‘rptree’ will use RandomProjectionTree
‘ball_tree’ will use BallTree
‘kd_tree’ will use KDTree
‘brute’ will use a brute-force search.
‘auto’ will attempt to decide the most appropriate exact algorithm based on the values passed to fit() method. This will not select an approximate nearest neighbor algorithm.

Note: fitting on sparse input will override the setting of this parameter, using brute force.

algorithm_params: dict, optional

Override default parameters of the NN algorithm. For example, with algorithm=’lsh’ and algorithm_params={n_candidates: 100} one hundred approximate neighbors are retrieved with LSH. If parameter hubness is set, the candidate neighbors are further reordered with hubness reduction. Finally, n_neighbors objects are used from the (optionally reordered) candidates.

hubness: {‘mutual_proximity’, ‘local_scaling’, ‘dis_sim_local’, None}, optional

Hubness reduction algorithm

‘mutual_proximity’ or ‘mp’ will use MutualProximity
‘local_scaling’ or ‘ls’ will use LocalScaling
‘dis_sim_local’ or ‘dsl’ will use DisSimLocal

If None, no hubness reduction will be performed (=vanilla kNN).

hubness_params: dict, optional

Override default parameters of the selected hubness reduction algorithm. For example, with hubness=’mp’ and hubness_params={‘method’: ‘normal’} a mutual proximity variant is used, which models distance distributions with independent Gaussians.

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 joblib.parallel_backend context. -1 means using all processors. See Glossary for more details. Doesn’t affect fit() method.

See also

RadiusNeighborsClassifier
KNeighborsRegressor
RadiusNeighborsRegressor
NearestNeighbors

Notes

See Nearest Neighbors in the scikit-learn 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

Examples

>>> X = [[0], [1], [2], [3]]
>>> y = [0, 0, 1, 1]
>>> from skhubness.neighbors import KNeighborsClassifier
>>> neigh = KNeighborsClassifier(n_neighbors=3)
>>> neigh.fit(X, y) 
KNeighborsClassifier(...)
>>> print(neigh.predict([[1.1]]))
[0]
>>> print(neigh.predict_proba([[0.9]]))
[[0.66666667 0.33333333]]

__init__(n_neighbors: int = 5, weights: str = 'uniform', algorithm: str = 'auto', algorithm_params: dict = None, hubness: str = None, hubness_params: dict = None, leaf_size: int = 30, p=2, metric='minkowski', metric_params=None, n_jobs=None, verbose: int = 0, **kwargs)[source]¶: Initialize self. See help(type(self)) for accurate signature.

Methods

`__init__`([n_neighbors, weights, algorithm, …])	Initialize self.
`fit`(X, y)	Fit the model using X as training data and y as target values
`get_params`([deep])	Get parameters for this estimator.
`kcandidates`([X, n_neighbors, return_distance])	Finds the K-neighbors of a point.
`kneighbors`([X, n_neighbors, return_distance])	TODO
`kneighbors_graph`([X, n_neighbors, mode])	Computes the (weighted) graph of k-Neighbors for points in X
`predict`(X)	Predict the class labels for the provided data
`predict_proba`(X)	Return probability estimates for the test data X.
`score`(X, y[, sample_weight])	Return the mean accuracy on the given test data and labels.
`set_params`(**params)	Set the parameters of this estimator.

fit(X, y)[source]¶

Fit the model using X as training data and y as target values

Parameters

X{array-like, sparse matrix, BallTree, KDTree, HNSW, FalconnLSH, PuffinLSH, NNG, RandomProjectionTree}: Training data. If array or matrix, shape [n_samples, n_features], or [n_samples, n_samples] if metric=’precomputed’.
y{array-like, sparse matrix}: Target values of shape = [n_samples] or [n_samples, n_outputs]

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

paramsmapping of string to any: Parameter names mapped to their values.

kcandidates(X=None, n_neighbors=None, return_distance=True) → numpy.ndarray[source]¶

Finds the K-neighbors of a point. Returns indices of and distances to the neighbors of each point.

Parameters

Xarray-like, shape (n_query, n_features), or (n_query, n_indexed) if metric == ‘precomputed’: The query point or points. If not provided, neighbors of each indexed point are returned. In this case, the query point is not considered its own neighbor.
n_neighborsint: Number of neighbors to get (default is the value passed to the constructor).
return_distanceboolean, optional. Defaults to True.: If False, distances will not be returned

Returns

distarray: Array representing the lengths to points, only present if return_distance=True
indarray: Indices of the nearest points in the population matrix.

Examples

In the following example, we construct a NeighborsClassifier class from an array representing our data set and ask who’s the closest point to [1,1,1]

>>> samples = [[0., 0., 0.], [0., .5, 0.], [1., 1., .5]]
>>> from skhubness.neighbors import NearestNeighbors
>>> neigh = NearestNeighbors(n_neighbors=1)
>>> neigh.fit(samples) 
NearestNeighbors(algorithm='auto', leaf_size=30, ...)
>>> print(neigh.kneighbors([[1., 1., 1.]])) 
(array([[0.5]]), array([[2]]))

As you can see, it returns [[0.5]], and [[2]], which means that the element is at distance 0.5 and is the third element of samples (indexes start at 0). You can also query for multiple points:

>>> X = [[0., 1., 0.], [1., 0., 1.]]
>>> neigh.kneighbors(X, return_distance=False) 
array([[1],
       [2]]...)

kneighbors(X=None, n_neighbors=None, return_distance=True)[source]¶: TODO

kneighbors_graph(X=None, n_neighbors=None, mode='connectivity')¶

Computes the (weighted) graph of k-Neighbors for points in X

Parameters

Xarray-like, shape (n_queries, n_features), or (n_queries, n_indexed) if metric == ‘precomputed’: The query point or points. If not provided, neighbors of each indexed point are returned. In this case, the query point is not considered its own neighbor.
n_neighborsint: Number of neighbors for each sample. (default is value passed to the constructor).
mode{‘connectivity’, ‘distance’}, optional: Type of returned matrix: ‘connectivity’ will return the connectivity matrix with ones and zeros, in ‘distance’ the edges are Euclidean distance between points.

Returns

Asparse graph in CSR format, shape = [n_queries, n_samples_fit]: n_samples_fit is the number of samples in the fitted data A[i, j] is assigned the weight of edge that connects i to j.