Using nested for loop to create a 3D matrix ?

Hello,

I have an ECG signal to parse to find values corresponding to a certain time window. The start and stop times of the window are respectively stored in QRSavgd and QRSavgf. X is my time scale.

B = [];
X = samples*1000/f;
A = horzcat(ECG(:,1:12),X.');
for i = 1:length(QRS)
    for j = 1:length(ECG)
        if A(j,13)>=QRSavgd(i) && A(j,13)<=QRSavgf(i)
            B(:,:,j) = vertcat(B,A(j,:));
            % plot(B);
        end
    end
end

I would like to store each B array found with the j loop in a 3D matrix so that I can differentiate each iteration of the j loop, to know which values I get when j=1, j=2...

Thanks

[Stephen23]

It does not make much sense to use both concatenation and indexing to collect your values:

B(:,:,j) = vertcat(B,A(j,:));

What are you hoping to achieve?

[Perrine Cristante]

I would like to be able to overlap the QRSs on a plot, hence getting each individual QRS in a 3D plot x,y,z where x is the ECG derivation, y is the amplitude and z is the QRS index.

Answer 1

[Perrine Cristante]

I finally found how to do it using cell arrays instead of 3D matrix, so I'll put the solution for the ones with the same problem as me :

B = {};
X = samples*1000/f;
A = horzcat(ECG(:,1:12),X.');
for i = 1:length(QRS)    
    C = [];
    for j = 1:length(ECG)
        if A(j,13)>=QRSavgd(i) && A(j,13)<=QRSavgf(i)
            C = vertcat(C,A(j,1:12));
        end
    end
    B{i} = C;
end

This creates a 2D matrix named C and stocks it in the cell array named B.