sklearn.neighbors
.KNeighborsRegressor¶
- class sklearn.neighbors.KNeighborsRegressor(n_neighbors=5, *, weights='uniform', algorithm='auto', leaf_size=30, p=2, metric='minkowski', metric_params=None, n_jobs=None)[source]¶
Regression based on k-nearest neighbors.
The target is predicted by local interpolation of the targets associated of the nearest neighbors in the training set.
Read more in the User Guide.
New in version 0.9.
- 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.
Uniform weights are used by default.
- 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. For a list of available metrics, see the documentation of
DistanceMetric
and the metrics listed insklearn.metrics.pairwise.PAIRWISE_DISTANCE_FUNCTIONS
. Note that the “cosine” metric usescosine_distances
. 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 ajoblib.parallel_backend
context.-1
means using all processors. See Glossary for more details. Doesn’t affectfit
method.
- Attributes
- effective_metric_str or callable
The distance metric to use. It will be same as the
metric
parameter or a synonym of it, e.g. ‘euclidean’ if themetric
parameter set to ‘minkowski’ andp
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 thep
parameter value if theeffective_metric_
attribute is set to ‘minkowski’.- n_features_in_int
Number of features seen during fit.
New in version 0.24.
- feature_names_in_ndarray of shape (
n_features_in_
,) Names of features seen during fit. Defined only when
X
has feature names that are all strings.New in version 1.0.
- n_samples_fit_int
Number of samples in the fitted data.
See also
NearestNeighbors
Unsupervised learner for implementing neighbor searches.
RadiusNeighborsRegressor
Regression based on neighbors within a fixed radius.
KNeighborsClassifier
Classifier implementing the k-nearest neighbors vote.
RadiusNeighborsClassifier
Classifier implementing a vote among neighbors within a given radius.
Notes
See Nearest Neighbors in the online documentation for a discussion of the choice of
algorithm
andleaf_size
.Warning
Regarding the Nearest Neighbors algorithms, if it is found that two neighbors, neighbor
k+1
andk
, have identical distances but different labels, the results will depend on the ordering of the training data.https://en.wikipedia.org/wiki/K-nearest_neighbors_algorithm
Examples
>>> X = [[0], [1], [2], [3]] >>> y = [0, 0, 1, 1] >>> from sklearn.neighbors import KNeighborsRegressor >>> neigh = KNeighborsRegressor(n_neighbors=2) >>> neigh.fit(X, y) KNeighborsRegressor(...) >>> print(neigh.predict([[1.5]])) [0.5]
Methods
fit
(X, y)Fit the k-nearest neighbors regressor from the training dataset.
get_params
([deep])Get parameters for this estimator.
kneighbors
([X, n_neighbors, return_distance])Find the K-neighbors of a point.
kneighbors_graph
([X, n_neighbors, mode])Compute the (weighted) graph of k-Neighbors for points in X.
predict
(X)Predict the target for the provided data.
score
(X, y[, sample_weight])Return the coefficient of determination of the prediction.
set_params
(**params)Set the parameters of this estimator.
- fit(X, y)[source]¶
Fit the k-nearest neighbors regressor 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
- selfKNeighborsRegressor
The fitted k-nearest neighbors regressor.
- 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]¶
Find 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]¶
Compute 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 distances between points, type of distance depends on the selected metric parameter in NearestNeighbors class.
- 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]
gives the weight of the edge connectingi
toj
. The matrix is of CSR format.
See also
NearestNeighbors.radius_neighbors_graph
Compute the (weighted) graph of Neighbors for points in X.
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 target 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), dtype=int
Target values.
- score(X, y, sample_weight=None)[source]¶
Return the coefficient of determination of the prediction.
The coefficient of determination \(R^2\) is defined as \((1 - \frac{u}{v})\), where \(u\) is the residual sum of squares
((y_true - y_pred)** 2).sum()
and \(v\) 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 ofy
, disregarding the input features, would get a \(R^2\) score of 0.0.- Parameters
- Xarray-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)
, wheren_samples_fitted
is the number of samples used in the fitting for the estimator.- yarray-like of shape (n_samples,) or (n_samples, n_outputs)
True values for
X
.- sample_weightarray-like of shape (n_samples,), default=None
Sample weights.
- Returns
- scorefloat
\(R^2\) of
self.predict(X)
wrt.y
.
Notes
The \(R^2\) score used when calling
score
on a regressor usesmultioutput='uniform_average'
from version 0.23 to keep consistent with default value ofr2_score
. This influences thescore
method of all the multioutput regressors (except forMultiOutputRegressor
).
- 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.