Find k-nearest neighbors using ExhaustiveSearcher object
IDX = knnsearch(NS,Y)
[IDX,D] = knnsearch(NS,Y)
[IDX,D] = knnsearch(NS,Y,'Name',Value)
IDX = knnsearch(NS,Y) finds the nearest neighbor (closest point) in NS.X for each point in Y. Rows of Y correspond to observations and columns correspond to features. Y must have the same number of columns as NS.X. IDX is a column vector with ny rows, where ny is the number of rows in Y. Each row in IDX contains the index of observation in NS.X which has the smallest distance to the corresponding observation in Y.
[IDX,D] = knnsearch(NS,Y) returns a column vector D containing the distances between each observation in Y and the corresponding closest observation in NS.X. That is, D(i) is the distance between NS.X(IDX(i),:) and Y(i,:).
[IDX,D] = knnsearch(NS,Y,'Name',Value) accepts one or more comma-separated argument name/value pairs. Specify Name inside single quotes.
A positive integer, k, specifying the number of nearest neighbors in NS.X for each point in Y. IDX and D are ny-by-k matrices. D sorts the distances in each row in ascending order. Each row in IDX contains the indices of the k closest neighbors in NS.X corresponding to the k smallest distances in D.
A logical value indicating whether knnsearch includes all the neighbors whose distance values are equal to the Kth smallest distance. If IncludeTies is true, knnsearch includes all these neighbors. In this case, IDX and D are ny-by-1 cell arrays. Each row in IDX and D contains a vector with at least K numeric numbers. D sorts the distances in each vector in ascending order. Each row in IDX contains the indices of the closest neighbors corresponding to these smallest distances in D.
For more information on these distance metrics, see Distance Metrics.
A positive scalar, p, indicating the exponent of the Minkowski distance. This parameter is only valid if knnsearch uses the 'minkowski' distance metric.
Default: NS.DistParameter if NS.Distance is 'minkowski' and 2 otherwise.
A positive definite matrix indicating the covariance matrix when computing the Mahalanobis distance. This parameter is only valid when knnsearch uses the 'mahalanobis' distance metric.
Default: NS.DistParameter if NS.Distance is 'mahalanobis', or nancov(X) otherwise.
A vector S with the length equal to the number of columns in X. Each coordinate of X and each query point is scaled by the corresponding element of S when computing the standardized Euclidean distance. This parameter is only valid when Distance is 'seuclidean'.
Find k-nearest neighbors of query data given training data using knnserach on an ExhaustiveSearcher model.
Load Fisher's iris data. Focus on the petal dimensions.
load fisheriris X = meas(:,3:4); % Predictors Y = species; % Response
Train a k-nearest neighbors searcher using the predictors. Specify to use the cosine distance.
ESMdl = ExhaustiveSearcher(X,'Distance','cosine')
ESMdl = ExhaustiveSearcher with properties: Distance: 'cosine' DistParameter:  X: [150x2 double]
ESMdl is an ExhaustiveSearcher model. You can access its properties using dot notation.
Find the 10 nearest neighbors from X to a query point (newpoint), first using the cosine, and then Mahalanobis distance metrics. The query point must have the same column dimension as the data used to train the model.
newpoint = [5 1.45]; [IdxCs,DCs] = knnsearch(ESMdl,newpoint,'k',10); [IdxMs,DMs] = knnsearch(ESMdl,newpoint,'k',10,... 'Distance','mahalanobis');
IdxCs and IdxMs are 1-by-10 matrices containing the row indices of X corresponding to the nearest neighbors to newpoint using cosine and Mahalanobis distances, respectively. Element (1,1) is the nearest, element (1,2) is the next nearest, and so on.
Plot the training data.
figure; gscatter(X(:,1),X(:,2),Y); title('Fisher''s Iris Data -- Nearest Neighbors'); xlabel('Petal length (cm)'); ylabel('Petal width (cm)'); hold on
Plot a cross for the query point.
Plot circles to identify the cosine nearest neighbors.
plot(X(IdxCs,1),X(IdxCs,2),'o','Color',[.5 .5 .5],'MarkerSize',10);
Plot pentagrams to identify the Mahalanobis nearest neighbors.
plot(X(IdxMs,1),X(IdxMs,2),'p','Color',[.5 .5 .5],'MarkerSize',10); legend('setosa','versicolor','virginica','query point',... 'cosine','mahalanobis','Location','Best'); hold off;
For information on a specific search algorithm, see Distance Metrics.