How can I plot a confusion matrix for a multi-class or non-binary classification problem?

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MathWorks Support Team 2017-5-1

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https://ww2.mathworks.cn/matlabcentral/answers/338244-how-can-i-plot-a-confusion-matrix-for-a-multi-class-or-non-binary-classification-problem

编辑： MathWorks Support Team 2018-3-16

I want to make a plot similar to the confusion matrix created in the Classification Learner app. This can make a confusion matrix for a multi-class or non-binary classification problem. In addition, it can plot things such as a True Positive or False Negative rates.

How can I do this?

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Answer 1

MathWorks Support Team 2017-7-5

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/338244-how-can-i-plot-a-confusion-matrix-for-a-multi-class-or-non-binary-classification-problem#answer_265257

Similar to the binary or two-class problem, this can be done using the "plotconfusion" function. By default, this command will also plot the True Positive, False Negative, Positive Predictive, and False Discovery rates in they grey-colored boxes. Please refer to the following example:

targetsVector = [1 2 1 1 3 2]; % True classes
outputsVector = [1 3 1 2 3 1]; % Predicted classes
% Convert this data to a [numClasses x 6] matrix
targets = zeros(3,6);
outputs = zeros(3,6);
targetsIdx = sub2ind(size(targets), targetsVector, 1:6);
outputsIdx = sub2ind(size(outputs), outputsVector, 1:6);
targets(targetsIdx) = 1;
outputs(outputsIdx) = 1;
% Plot the confusion matrix for a 3-class problem
plotconfusion(targets,outputs)

The class labels can be customized by setting that 'XTickLabel' and 'YTickLabel' properties of the axis:

h = gca;
h.XTickLabel = {'Class A','Class B','Class C',''};
h.YTickLabel = {'Class A','Class B','Class C',''};
h.YTickLabelRotation = 90;

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Michael Abboud 2017-7-6

I have updated the above answer to better indicate that the 'TargetsVector' contains the true class labels.

I also included a quick example in the answer showing how to add strings as a name for each class, as I think that is a great easy way to make the plot more easily interpretable

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Answer 2

David Franco 2018-1-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/338244-how-can-i-plot-a-confusion-matrix-for-a-multi-class-or-non-binary-classification-problem#answer_301270

编辑：MathWorks Support Team 2018-3-16

在 MATLAB Online 中打开

Implementation code:

Confusion Matrix

function [] = confusion_matrix(T,Y)
M = size(unique(T),2);
N = size(T,2);
targets = zeros(M,N);
outputs = zeros(M,N);
targetsIdx = sub2ind(size(targets), T, 1:N);
outputsIdx = sub2ind(size(outputs), Y, 1:N);
targets(targetsIdx) = 1;
outputs(outputsIdx) = 1;
% Plot the confusion matrix
plotconfusion(targets,outputs)