我编写了以下代码来获得我的KNN分类器的ROC图:
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);
然后我们可以绘制FPR vs TPR来得到ROC曲线。
然而,FPR和TPR与我使用自己的实现得到的不同,上面的代码不会显示所有的点,实际上,上面的代码只显示ROC上的三个点。我实现的代码将在ROC上显示151个点,因为数据的大小为150。
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];
我可以问一下如何调整' perfcurve
'以使其输出ROC的所有点吗?非常感谢。
a .
我不熟悉perfcurve
,但您是否尝试过使用MALAB帮助。在MATLAB工作空间只是类型:help perfcurve
,你得到很多帮助那里。在MATWORKS网站上也有帮助页面,例如您的案例,请查看:http://www.mathworks.com/help/stats/perfcurve.html