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Helping with Matlab error Invalid training data. Predictors must be a cell array of sequences. The data dimension of all sequences must be the same.

Asked by Hossam Elshahaby on 16 Sep 2018 at 19:18
Latest activity Commented on by Hossam Elshahaby on 20 Sep 2018 at 6:49

Hello Mr/Ms,

I have the following code to create a data set from 131 video each has 2000 images where each of them has size 40*200

I want to create RNN and train it so that each video has its label -> ex horizontal , vertical motion etc

I got the error : "Invalid training data. Predictors must be a cell array of sequences. The data dimension of all sequences must be the same." but I believe the XTrain is cell array of sequences and The data dimension of all sequences are the same.

I saw several not answered questions in the community asking the same question . Is it a matlab issue ? if yes, is there a workaround?

newsDatasetPath = fullfile(matlabroot,'NewsDataSetCaptionType');
Labels = dir(newsDatasetPath);
Yactual = strings(131);
X = cell([131 1]) ;
VideoNumber = 0;
% Loop over filenames, inserting the image.
for slice = 3 : length(Labels)
      LabelsPath = fullfile(newsDatasetPath, Labels(slice).name);
      Videos = dir(LabelsPath);
      for VideoIndex = 3 : length(Videos)
          VideosPath = fullfile(LabelsPath, Videos(VideoIndex).name);
          Files = dir(VideosPath);
          VideoNumber = VideoNumber + 1;
          array2d = zeros(8000,2000); 
          for FileIndex = 3 : length(Files)
              filename = fullfile(VideosPath, Files(FileIndex).name);
              thisImage = imread(filename);
              thisImage_Reshapped = reshape(thisImage,[8000,1]);
              % Image is okay.  Insert it.
              array2d( 1:8000,FileIndex-2) = thisImage_Reshapped;
          end
          array2d_ts = timeseries(array2d);
          X{VideoNumber} = array2d_ts;
          Yactual( VideoNumber  ) = categorical(string(Labels(slice).name)); 
      end
end
n = 131;
Order = randperm(n) ;
X_shuffled = X(Order,1);
Yactual_shuffled = Yactual(Order,1);
trainNumFiles = floor(0.7 * n );
XTrain = X_shuffled(1:trainNumFiles,:);
YTrain = Yactual_shuffled(1:trainNumFiles,:);
XTest = X_shuffled(trainNumFiles+1:end,:);
YTest = Yactual_shuffled(trainNumFiles+1:end,:);
% Not: For sequence-to-label classification networks, the output mode of the last LSTM layer must be 'last'.
inputSize = 2000;
numHiddenUnits1 = 125;
numHiddenUnits2 = 100;
numClasses = 4;
maxEpochs = 100;
miniBatchSize = 27;
layers = [ ...
      sequenceInputLayer(inputSize , 'Name','InputLayer' )
      lstmLayer(numHiddenUnits1,'OutputMode','sequence' ,'Name','LSTM_Layer1')
      lstmLayer(numHiddenUnits2,'OutputMode','last' ,'Name','LSTM_Layer2')
      fullyConnectedLayer( numClasses ,'Name','Fully_Connected_Layer')
      softmaxLayer('Name','Softmax_Layer')
      classificationLayer('Name','Classification_Layer')
      ];
options = trainingOptions('sgdm', ...
    'ExecutionEnvironment','auto', ...
    'InitialLearnRate',0.01, ...
    'LearnRateSchedule','piecewise', ...
    'LearnRateDropPeriod',20, ...    
    'MaxEpochs',maxEpochs, ...
    'MiniBatchSize',miniBatchSize, ...
    'SequenceLength','longest', ...
    'Shuffle','never', ...
    'Verbose',0, ...
    'Plots','training-progress');
net = trainNetwork( XTrain , categorical(YTrain) , layers , options);
predictedLabels = classify( net , XTest , ...
    'MiniBatchSize',miniBatchSize  , ...
    'SequenceLength','longest' ) ;
% accuracy = (TP + TN)/(TP + FP + FN + TN) ; the average accuracy is returned 
accuracy = sum(predictedLabels == valLabels)/numel(valLabels)
RNN_Net17b = net;
view(net)
save RNN_LSTM_Net17b  % retrieve using load(net)

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1 Answer

Answer by Conor Daly on 19 Sep 2018 at 13:43
 Accepted Answer

Thanks for sharing your code. timeseries objects are not accepted into trainNetwork, so you do not need to convert your numeric sequences into timeseries when preparing your data. Allocating array2d into X should create an appropriate cell array for trainNetwork

X{VideoNumber} = array2d;

Looking at your network architecture I noticed another issue. The inputSize argument of sequenceInputLayer should not correspond to the number of time steps in your data. Instead, inputSize is the fixed data dimension of your sequences, so it should be 40*200 = 8000 to fit with your data. Networks with a sequenceInputLayer can accept an arbitrary number of time steps, so if you had a video which had fewer than 2000 frames, the network would still be able to determine a classification for the video.

  1 Comment

Thank you for answering my question.

"Helping with Matlab error Invalid training data. Predictors must be a cell array of sequences. The data dimension of all sequences must be the same."

New code:

inputSize = 8000;
numHiddenUnits = 125;
numClasses = 4; 
maxEpochs = 300;
miniBatchSize = 15;
layers = [ ...
    sequenceInputLayer(inputSize , 'Name','InputLayer' )
    lstmLayer(numHiddenUnits,'OutputMode','last' ,'Name','LSTM_Layer1')
    fullyConnectedLayer( numClasses ,'Name','Fully_Connected_Layer')
    softmaxLayer('Name','Softmax_Layer')
    classificationLayer('Name','Classification_Layer')
    ];
options = trainingOptions('sgdm', ...
    'ExecutionEnvironment','auto', ...
    'InitialLearnRate',0.000003, ...
    'LearnRateSchedule','piecewise', ...
    'MaxEpochs',maxEpochs, ...
    'MiniBatchSize',miniBatchSize, ...
    'SequenceLength','longest', ...
    'Shuffle','never', ...
    'Verbose',0, ...
    'Plots','training-progress');
net = trainNetwork( XTrain , categorical(YTrain') , layers , options);
predictedLabels = classify( net , XTest , ...
    'MiniBatchSize',miniBatchSize  , ...
    'SequenceLength','longest' ) ;
% accuracy = (TP + TN)/(TP + FP + FN + TN) ; the average accuracy is returned 
accuracy = sum(predictedLabels == categorical(YTest'))/numel(YTest)

I accepted your answer it today. I got accuracy 80% how can I raise it ?

Could you give me some ideas , please?

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