mcdownsampling.m

一个matlab的工具包,里面包括一些分类器 例如 KNN KMEAN SVM NETLAB 等等有很多.

function  [Y_compute, Y_prob] = DownSampling(classifier, para, X_train, Y_train, X_test, Y_test, num_class)

class_set = GetClassSet(Y_train);
p = str2num(char(ParseParameter(para, {'-PosNegRatio'}, {'0.5'})));
sizefactor = p(1);

if (num_class ~= 2), 
    fprintf('Error: The number of classes is larger than 2!');
    return;
end;
    
num_positive = sum(Y_train == class_set(1));
num_negative = sum(Y_train ~= class_set(1));

data_neg = [];
data_pos = [];

for j = 1:size(Y_train, 1)
    if (Y_train(j) ~= class_set(1))   
        data_neg = [data_neg; X_train(j, :)];      
    else
        data_pos = [data_pos; X_train(j, :)]; 
    end;    
end;
       
downsize = fix((1 - sizefactor) / sizefactor * num_positive);
rand_index = fix(rand(1, downsize) * size(data_neg, 1)) + 1;
data_additional = data_neg(rand_index, :);     
X_train = [data_pos; data_additional];
       
label_pos = ones(size(data_pos, 1), 1) * class_set(1);
label_additional = ones(size(data_additional, 1), 1) * class_set(2);
Y_train = [label_pos; label_additional];       

[Y_compute, Y_prob] = Classify(classifier, X_train, Y_train, X_test, Y_test, num_class);