sklearn.neighbors.KNeighborsClassifier  
class sklearn.neighbors.KNeighborsClassifier(n_neighbors=5, *, weights='uniform', algorithm='auto', leaf_size=30, p=2, metric='minkowski', metric_params=None, n_jobs=None, **kwargs) [source]
 
Classifier implementing the k-nearest neighbors vote. Read more in the User Guide.  Parameters 
 
n_neighborsint, default=5 

Number of neighbors to use by default for kneighbors queries.  
weights{‘uniform’, ‘distance’} or callable, 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’}, default=’auto’ 

Algorithm used to compute the nearest neighbors:  ‘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 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_sizeint, 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.  
pint, 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.  
metricstr 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 DistanceMetric for a list of available metrics. If metric is “precomputed”, X is assumed to be a distance matrix and must be square during fit. X may be a sparse graph, in which case only “nonzero” elements may be considered neighbors.  
metric_paramsdict, default=None 

Additional keyword arguments for the metric function.  
n_jobsint, 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.    Attributes 
 
classes_array of shape (n_classes,) 

Class labels known to the classifier  
effective_metric_str or callble 

The distance metric used. It will be same as the metric parameter or a synonym of it, e.g. ‘euclidean’ if the metric parameter set to ‘minkowski’ and p parameter set to 2.  
effective_metric_params_dict 

Additional keyword arguments for the metric function. For most metrics will be same with metric_params parameter, but may also contain the p parameter value if the effective_metric_ attribute is set to ‘minkowski’.  
n_samples_fit_int 

Number of samples in the fitted data.  
outputs_2d_bool 

False when y’s shape is (n_samples, ) or (n_samples, 1) during fit otherwise True.      See also  
RadiusNeighborsClassifier


KNeighborsRegressor


RadiusNeighborsRegressor


NearestNeighbors

  Notes See 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 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)
KNeighborsClassifier(...)
>>> print(neigh.predict([[1.1]]))
[0]
>>> print(neigh.predict_proba([[0.9]]))
[[0.66666667 0.33333333]]
 Methods  
fit(X, y) Fit the k-nearest neighbors classifier from the training dataset.  
get_params([deep]) Get parameters for this estimator.  
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.  
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 k-nearest neighbors classifier from the training dataset.  Parameters 
 
X{array-like, sparse matrix} of shape (n_samples, n_features) or (n_samples, n_samples) if metric=’precomputed’ 

Training data.  
y{array-like, sparse matrix} of shape (n_samples,) or (n_samples, n_outputs) 

Target values.    Returns 
 
selfKNeighborsClassifier 

The fitted k-nearest neighbors classifier.     
  
get_params(deep=True) [source]
 
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 
 
paramsdict 

Parameter names mapped to their values.     
  
kneighbors(X=None, n_neighbors=None, return_distance=True) [source]
 
Finds the K-neighbors of a point. Returns indices of and distances to the neighbors of each point.  Parameters 
 
Xarray-like, shape (n_queries, n_features), or (n_queries, n_indexed) if metric == ‘precomputed’, default=None 

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, default=None 

Number of neighbors required for each sample. The default is the value passed to the constructor.  
return_distancebool, default=True 

Whether or not to return the distances.    Returns 
 
neigh_distndarray of shape (n_queries, n_neighbors) 

Array representing the lengths to points, only present if return_distance=True  
neigh_indndarray of shape (n_queries, n_neighbors) 

Indices of the nearest points in the population matrix.     Examples In the following example, we construct a NearestNeighbors 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(n_neighbors=1)
>>> 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=None, n_neighbors=None, mode='connectivity') [source]
 
Computes the (weighted) graph of k-Neighbors for points in X  Parameters 
 
Xarray-like of shape (n_queries, n_features), or (n_queries, n_indexed) if metric == ‘precomputed’, default=None 

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. For metric='precomputed' the shape should be (n_queries, n_indexed). Otherwise the shape should be (n_queries, n_features).  
n_neighborsint, default=None 

Number of neighbors for each sample. The default is the value passed to the constructor.  
mode{‘connectivity’, ‘distance’}, default=’connectivity’ 

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-matrix of 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. The matrix is of CSR format.      See also  
NearestNeighbors.radius_neighbors_graph

  Examples >>> X = [[0], [3], [1]]
>>> from sklearn.neighbors import NearestNeighbors
>>> neigh = NearestNeighbors(n_neighbors=2)
>>> neigh.fit(X)
NearestNeighbors(n_neighbors=2)
>>> A = neigh.kneighbors_graph(X)
>>> A.toarray()
array([[1., 0., 1.],
       [0., 1., 1.],
       [1., 0., 1.]])
 
  
predict(X) [source]
 
Predict the class labels for the provided data.  Parameters 
 
Xarray-like of shape (n_queries, n_features), or (n_queries, n_indexed) if metric == ‘precomputed’ 

Test samples.    Returns 
 
yndarray of shape (n_queries,) or (n_queries, n_outputs) 

Class labels for each data sample.     
  
predict_proba(X) [source]
 
Return probability estimates for the test data X.  Parameters 
 
Xarray-like of shape (n_queries, n_features), or (n_queries, n_indexed) if metric == ‘precomputed’ 

Test samples.    Returns 
 
pndarray of shape (n_queries, 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.     
  
score(X, y, sample_weight=None) [source]
 
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 
 
Xarray-like of shape (n_samples, n_features) 

Test samples.  
yarray-like of shape (n_samples,) or (n_samples, n_outputs) 

True labels for X.  
sample_weightarray-like of shape (n_samples,), default=None 

Sample weights.    Returns 
 
scorefloat 

Mean accuracy of self.predict(X) wrt. y.     
  
set_params(**params) [source]
 
Set the parameters of this estimator. The method works on simple estimators as well as on nested objects (such as Pipeline). The latter have parameters of the form <component>__<parameter> so that it’s possible to update each component of a nested object.  Parameters 
 
**paramsdict 

Estimator parameters.    Returns 
 
selfestimator instance 

Estimator instance.     
 
 Examples using sklearn.neighbors.KNeighborsClassifier
 
  Release Highlights for scikit-learn 0.24  

  Classifier comparison  

  Plot the decision boundaries of a VotingClassifier  

  Nearest Neighbors Classification  

  Caching nearest neighbors  

  Comparing Nearest Neighbors with and without Neighborhood Components Analysis  

  Dimensionality Reduction with Neighborhood Components Analysis  

  Digits Classification Exercise  

  Classification of text documents using sparse features