9.4.4. sklearn.neighbors.NeighborsClassifier¶

class sklearn.neighbors.NeighborsClassifier(*args, **kwargs)¶

Classifier implementing the nearest neighbors vote. (Deprecated)

DEPRECATED IN VERSION 0.9; WILL BE REMOVED IN VERSION 0.11 Please use KNeighborsClassifier or RadiusNeighborsClassifier instead.

Samples participating in the vote are either the k-nearest neighbors (for some k) or all neighbors within some fixed radius around the sample to classify.

Parameters :

n_neighbors : int, optional (default = 5)

Number of neighbors to use by default for k_neighbors queries.

radius : float, optional (default = 1.0)

Range of parameter space to use by default for :meth`radius_neighbors` queries.

algorithm : {‘auto’, ‘ball_tree’, ‘kd_tree’, ‘brute’}, optional

Algorithm used to compute the nearest neighbors:

‘ball_tree’ will use BallTree

‘kd_tree’ will use scipy.spatial.cKDtree

‘brute’ will use a brute-force search.

‘auto’ will attempt to decide the most appropriate algorithm based on the values passed to 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 cKDTree. 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.

classification_type : {‘knn_vote’, ‘radius_vote’}, optional

Type of fit to use: ‘knn_vote’ specifies a k-NN classification. ‘radius_vote’ specifies a r-NN classification. Default is ‘knn_vote’.

Notes

See Nearest Neighbors in the online documentation for a discussion of the choice of algorithm and leaf_size.

References

http://en.wikipedia.org/wiki/K-nearest_neighbor_algorithm

Examples

>>> X = [[0], [1], [2], [3]]
>>> y = [0, 0, 1, 1]
>>> from sklearn.neighbors import NeighborsClassifier
>>> neigh = NeighborsClassifier(n_neighbors=2)
>>> neigh.fit(X, y)
NeighborsClassifier(algorithm='auto', classification_type='knn_vote',
          leaf_size=30, n_neighbors=2, radius=1.0)
>>> print neigh.predict([[1.5]])
[0]

Methods

`fit`(X, y)	Fit the model using X as training data and y as target values
`kneighbors`(X[, n_neighbors, return_distance])	Finds the K-neighbors of a point.
`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
`radius_neighbors`(X[, radius, return_distance])	Finds the neighbors of a point within a given radius.
`radius_neighbors_graph`(X[, radius, mode])	Computes the (weighted) graph of Neighbors for points in X
`score`(X, y)	Returns the mean error rate on the given test data and labels.
`set_params`(**params)	Set the parameters of the estimator.

__init__(*args, **kwargs)¶: DEPRECATED: deprecated in v0.9; will be removed in v0.11; use KNeighborsClassifier or RadiusNeighborsClassifier instead

fit(X, y)¶

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

Parameters :

X : {array-like, sparse matrix, BallTree, cKDTree}

Training data. If array or matrix, then the shape is [n_samples, n_features]

y : {array-like, sparse matrix}, shape = [n_samples]

Target values, array of integer values.

kneighbors(X, n_neighbors=None, return_distance=True)¶

Finds the K-neighbors of a point.

Returns distance

Parameters :

X : array-like, last dimension same as that of fit data

The new point.

n_neighbors : int

Number of neighbors to get (default is the value passed to the constructor).

return_distance : boolean, optional. Defaults to True.

If False, distances will not be returned

Returns :

dist : array

Array representing the lengths to point, only present if return_distance=True

ind : array

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 sklearn.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_graph(X, n_neighbors=None, mode='connectivity')¶

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

Parameters :

X : array-like, shape = [n_samples, n_features]

Sample data

n_neighbors : int

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 :

A : sparse matrix in CSR format, shape = [n_samples, 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.

Examples

>>> X = [[0], [3], [1]]
>>> from sklearn.neighbors import NearestNeighbors
>>> neigh = NearestNeighbors(n_neighbors=2)
>>> neigh.fit(X) 
NearestNeighbors(algorithm='auto', leaf_size=30, ...)
>>> A = neigh.kneighbors_graph(X)
>>> A.todense()
matrix([[ 1.,  0.,  1.],
        [ 0.,  1.,  1.],
        [ 1.,  0.,  1.]])

predict(X)¶

Predict the class labels for the provided data

Parameters :

X: array :

A 2-D array representing the test points.

Returns :

labels: array :

List of class labels (one for each data sample).

radius_neighbors(X, radius=None, return_distance=True)¶

Finds the neighbors of a point within a given radius.

Returns distance

Parameters :

X : array-like, last dimension same as that of fit data

The new point.

radius : float

Limiting distance of neighbors to return. (default is the value passed to the constructor).

return_distance : boolean, optional. Defaults to True.

If False, distances will not be returned

Returns :

dist : array

Array representing the lengths to point, only present if return_distance=True

ind : array

Indices of the nearest points in the population matrix.

Examples

In the following example, we construnct 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 sklearn.neighbors import NearestNeighbors
>>> neigh = NearestNeighbors(radius=1.6)
>>> neigh.fit(samples) 
NearestNeighbors(algorithm='auto', leaf_size=30, ...)
>>> print neigh.radius_neighbors([1., 1., 1.]) 
(array([[ 1.5,  0.5]]...), array([[1, 2]]...)

The first array returned contains the distances to all points which are closer than 1.6, while the second array returned contains their indices. In general, multiple points can be queried at the same time. Because the number of neighbors of each point is not necessarily equal, radius_neighbors returns an array of objects, where each object is a 1D array of indices.

radius_neighbors_graph(X, radius=None, mode='connectivity')¶

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

Neighborhoods are restricted the points at a distance lower than radius.

Parameters :

X : array-like, shape = [n_samples, n_features]

Sample data

radius : float

Radius of neighborhoods. (default is the 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 :

A : sparse matrix in CSR format, shape = [n_samples, n_samples]

A[i, j] is assigned the weight of edge that connects i to j.

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9.4.4. sklearn.neighbors.NeighborsClassifier¶