I am having an error in running this code. Kindly help.

Below is the error message received when I ran the classifier section of the code:

Error in SimpleFaceRecognition (line 39)
        trainingFeatures(featureCount,:) = extractHOGFeatures(read(training(i),j));

Undefined function or variable 'trainingLabel'.

Error in SimpleFaceRecognition (line 47)
faceClassifier = fitcecoc(trainingFeatures,trainingLabel);

%%Load Image Information from ATT Face Database Directory
faceDatabase = imageSet('orl_faces','recursive');

%%Display Montage of First Face
figure;
montage(faceDatabase(1).ImageLocation);
title('Images of Single Face');

Display Query Image and Database Side-Side

personToQuery = 1;
galleryImage = read(faceDatabase(personToQuery),1);
figure;
for i=1:size(faceDatabase,2)
imageList(i) = faceDatabase(i).ImageLocation(5);
end
subplot(1,2,1);imshow(galleryImage);
subplot(1,2,2);montage(imageList);
diff = zeros(1,9);

%%Split Database into Training & Test Sets
[training,test] = partition(faceDatabase,[0.8 0.2]);

%%Extract and display Histogram of Oriented Gradient Features for single face 
person = 5;
[hogFeature, visualization]= ...
    extractHOGFeatures(read(training(person),1));
figure;
subplot(2,1,1);imshow(read(training(person),1));title('Input Face');
subplot(2,1,2);plot(visualization);title('HoG Feature');

%%Extract HOG Features for training set 
trainingFeatures = zeros(size(training,2)*training(1).Count,4680);
featureCount = 1;
for i=1:size(training,2)
    for j = 1:training(i).Count
        trainingFeatures(featureCount,:) = extractHOGFeatures(read(training(i),j));
        trainingLabel{featureCount} = training(i).Description;    
        featureCount = featureCount + 1;
    end
    personIndex{i} = training(i).Description;
end

%%Create 40 class classifier using fitcecoc 
faceClassifier = fitcecoc(trainingFeatures,trainingLabel);

[Geoff Hayes]

Chidibere - it looks like your trainingLabel variable is only initialized and updated within the for loop. So if your code does not enter that loop then this variable will be undefined. I suggest that you put a breakpoint at the line

 for i=1:size(training,2)

and then run your code. What are the dimensions of training? What is the value of training(i).Count? Does your code ever reach the line

 trainingLabel{featureCount} = training(i).Description;

Also, it is good practice to assign something to this variable outside of your for loop....even if it is just simply

 trainingLabel = [];

just so that you can avoid error like this in the future.

[Chidiebere Ike]

Thanks so much for you response. I appreciate. I have tried correcting and re-running the codes again. I am still faced with error at this point of the code. Please guide me on this aspect. Below is thew error message:

*Subscripted assignment dimension mismatch.

Error in SimpleFaceRecognition (line 40) trainingFeatures(featureCount,:) = extractHOGFeatures(read(training(i),j));*

%% Extract HOG Features for training set

trainingFeatures = zeros(size(training,2)*training(1).Count,4680);

featureCount = 1; trainingLabel = []; for i=1:size(training,2) ** Break point

    trainingLabel{featureCount} = training(i).Description;

    for j = 1:training(i).Count
        trainingFeatures(featureCount,:) = extractHOGFeatures(read(training(i),j));    
        featureCount = featureCount + 1;
    end
    personIndex{i} = training(i).Description;

end *** ** Break point

[Geoff Hayes]

Should trainingFeatures be a cell array? what are the dimensions of the object that you are assigning to this array? will the dimensions be the same for each iteration of the loop? From https://www.mathworks.com/matlabcentral/answers/93586-why-do-i-get-the-subscripted-assignment-dimension-mismatch-error-message,

This error occurs when you attempt to assign elements to an existing array, but the size of the variable you are trying to assign is not compatible with the existing array.