I am trying to get Matlab Minibatchqueue to spit out 500 rows per column, from a 16 columns (variable ds) at a time

Question

I have an EEG with 16 chanel. It is organized in a table using TabularTextDatastore. 16 columns, one per chanel. I want to organize the data in minibatchs 500x16 datapoints. Each datapoint count for a signal mesuments at 1 sec interval.

ds[100000 X 16] -> minibatchqueue -> [80000] -> model || [ch1ch2ch3...n] || [500 500 500 500 ...]

model has 500x16=80000 inputs in the feature layer

this is m minibacthqueue code:

mbq = minibatchqueue(ds, ...
                     MiniBatchSize=miniBatchSize, ...
                     PartialMiniBatch="discard", ...
                     MiniBatchFcn=@preprocessMiniBatch, ...
                     MiniBatchFormat="SSCB");

the preprocessMiniBatch function I can't figure out. How do I manipulate the date so it spits out 500 seconds of each channel to my model. The alternative is to to create 16 identical models that can process 1 chanel at a time.

I tried:

function X = preprocessMiniBatch(data)
    % Concatenate mini-batch
    X = data{1,1:500};

    for idx = 2:16
        X = cat(1,X,data{idx,1:500});
    end

end

the ouput is this:

Error using minibatchqueue>iValidateMiniBatchFcn (line 778) Number of mini-batch variables (16) must be less than or equal to the number of outputs (1) of function specified by 'MiniBatchFcn'. Set number of mini-batch variables or modify the number of outputs of the function.

Error in minibatchqueue>iParseInputs (line 656) iValidateMiniBatchFcn(options.MiniBatchFcn, numVariables, options.NumOutputs);

Error in minibatchqueue (line 294) options = iParseInputs(numVariables, varargin{:});

Error in eegbtexp (line 66) mbq = minibatchqueue(ds, ...