我需要一个具有描述性的示例,展示如何在一个两类数据集上进行10折SVM分类。MATLAB文档中只有一个示例,但没有10折。有人能帮我吗?
我需要一个具有描述性的示例,展示如何在一个两类数据集上进行10折SVM分类。MATLAB文档中只有一个示例,但没有10折。有人能帮我吗?
这里是一个完整的示例,使用了生物信息学工具箱中的以下函数:SVMTRAIN、SVMCLASSIFY、CLASSPERF和CROSSVALIND。
load fisheriris %# load iris dataset
groups = ismember(species,'setosa'); %# create a two-class problem
%# number of cross-validation folds:
%# If you have 50 samples, divide them into 10 groups of 5 samples each,
%# then train with 9 groups (45 samples) and test with 1 group (5 samples).
%# This is repeated ten times, with each group used exactly once as a test set.
%# Finally the 10 results from the folds are averaged to produce a single
%# performance estimation.
k=10;
cvFolds = crossvalind('Kfold', groups, k); %# get indices of 10-fold CV
cp = classperf(groups); %# init performance tracker
for i = 1:k %# for each fold
testIdx = (cvFolds == i); %# get indices of test instances
trainIdx = ~testIdx; %# get indices training instances
%# train an SVM model over training instances
svmModel = svmtrain(meas(trainIdx,:), groups(trainIdx), ...
'Autoscale',true, 'Showplot',false, 'Method','QP', ...
'BoxConstraint',2e-1, 'Kernel_Function','rbf', 'RBF_Sigma',1);
%# test using test instances
pred = svmclassify(svmModel, meas(testIdx,:), 'Showplot',false);
%# evaluate and update performance object
cp = classperf(cp, pred, testIdx);
end
%# get accuracy
cp.CorrectRate
%# get confusion matrix
%# columns:actual, rows:predicted, last-row: unclassified instances
cp.CountingMatrix
输出结果为:
ans =
0.99333
ans =
100 1
0 49
0 0
我们仅有一个“setosa”实例分类错误为“non-setosa”,获得了99.33%
的准确率。
更新:SVM函数已经在R2013a版本中移至统计工具箱。
cp.CountingMatrix
绘制图形吗?@Amro - Tariq Khalifabar3
来绘制混淆矩阵。如果你有神经网络工具箱,那么就有plotconfusion
函数,否则你可以手动操作,像这样:https://dev59.com/aVrUa4cB1Zd3GeqPik8g#7081430 - Amrocp
对象。然后在循环内部,我们使用当前验证折叠的预测更新cp
对象。每次调用该函数时,它都会累积结果。因此,当我们完成循环时,返回的结果将是K折交叉验证的平均值。顺便说一下,名字是Amro而不是Arno :) - Amrocp.CorrectRate
返回分类准确率的 当前滚动平均值,而非当前折叠的分类准确率。如果您想要后者,请使用cp.LastCorrectRate
。 - Amro