我写了以下代码来获取我的KNN分类器的ROC曲线图:
可以请教一下如何调整'
答案:
load fisheriris;
features = meas;
featureSelcted = features;
numFeatures = size(meas,1);
%% Define ground truth
groundTruthGroup = species;
%% Construct a KNN classifier
KNNClassifierObject = ClassificationKNN.fit(featureSelcted, groundTruthGroup, 'NumNeighbors', 3, 'Distance', 'euclidean');
% Predict resubstitution response of k-nearest neighbor classifier
[KNNLabel, KNNScore] = resubPredict(KNNClassifierObject);
% Fit probabilities for scores
groundTruthNumericalLable = [ones(50,1); zeros(50,1); -1.*ones(50,1)];
[FPR, TPR, Thr, AUC, OPTROCPT] = perfcurve(groundTruthNumericalLable(:,1), KNNScore(:,1), 1);
我们可以绘制FPR与TPR的图像,得到ROC曲线。
然而,使用上述代码所得到的FPR和TPR与我使用自己的实现所得到的结果不同,上述代码并不会显示所有的点,实际上上述代码只会在ROC曲线上显示三个点。由于数据集的大小为150,我实现的代码将显示151个点。
patternsKNN = [KNNScore(:,1), groundTruthNumericalLable(:,1)];
patternsKNN = sortrows(patternsKNN, -1);
groundTruthPattern = patternsKNN(:,2);
POS = cumsum(groundTruthPattern==1);
TPR = POS/sum(groundTruthPattern==1);
NEG = cumsum(groundTruthPattern==0);
FPR = NEG/sum(groundTruthPattern==0);
FPR = [0; FPR];
TPR = [0; TPR];
可以请教一下如何调整'
perfcurve
',使其输出ROC曲线上的所有点吗?非常感谢。答案: