matlab的kNN

 

knnsearch

Find k-nearest neighbors using dataexpand all in page Syntax IDX = knnsearch(X,Y) [IDX,D] = knnsearch(X,Y) [IDX,D] = knnsearch(X,Y,'Name',Value)

Description

IDX = knnsearch(X,Y) finds the nearest neighbor in X for each point in Y. X is an mx-by-n matrix and Y is an my-by-n matrix. Rows of X and Y correspond to observations and columns correspond to variables. IDX is a column vector with my rows. Each row in IDX contains the index of nearest neighbor in X for the corresponding row in Y.

[IDX,D] = knnsearch(X,Y) returns an my-by-1 vector D containing the distances between each observation in Y and the corresponding closest observation in X. That is, D(i) is the distance between X(IDX(i),:) and Y(i,:).

[IDX,D] = knnsearch(X,Y,'Name',Value) accepts one or more optional comma-separated name/value pairs. Specify Name inside single quotes.

 

 

 

 

 knnsearch，能输出knn的最近邻的下标，如

 [n,d] = knnsearch(x,newpoint,'k',10); %Find the 10 sample points closest to the new point.

 

newpoint2 = [5 1.45;6 2;2.75 .75]; 

[n2,d2] = knnsearch(x,newpoint2,'k',10); %

输入参数分别是，已知样本，新样本，参数名称及值。新样本可以包含多个，已知样本不包含类别，与

输出参数是，最近邻的下标及与新样本的距离。

 

 

Find the species of the 10 neighbors.

tabulate(species(n))

用于输出统计指标。

 

注意：

For a fixed positive integer K, knnsearch finds the K points in X that are nearest each point in Y. In contrast, for a fixed positive real value r, rangesearch finds all the points in X that are within a distance r of each point in Y.

knnsearch找到最近的k个邻居，而rangesearch找到一定范围内的所有点，二者既相关又不同。其格式与knnsearch类似

idx = rangesearch(X,Y,r)
[idx,D]= rangesearch(X,Y,r)
[idx,D]= rangesearch(X,Y,r,Name,Value)