Real time growing table. Should I use table, double array, cell array..?

I am reading data from a serialport using Callback.

So every line of data is a 'double 1x3' like:

new_line = [time distance RSSI]

Every second I get around 6-8 lines and I need to store them and plot in real time ( plot(time,distance) )

It can be easily done with matrix like:

M(end+1,:)=new_line

However, I have to separate into 8 different matrix because the data is gathered from different sources. One easy way is to make 8 different matrix (M1, M2... M8)

But I wonder if I can store all in the same variable (a table)? The goal would be something looking like this:

T =

  8×2 table

                 M1                               M2              
    _____________________________    _____________________________

    0.20619        249        -35    0.53786        257        -35
      1.214        249        -35     1.5412        238        -35
     2.2208        221        -35      2.537        235        -35
     3.2199        262        -35     3.5289        268        -35
     4.2186        240        -35     4.5363        226        -35
     5.2124        252        -35      5.557        244        -35
     6.2206        226        -35     6.5375        230        -35
     7.2237        242        -35     7.5445        230        -35

But for 8 different variables, and increasing rows (size not known before hand)

But then, how do I store every new line of data in the specific "source" column, without affecting the other sources column? Am I in the wrong direction?

Thank you very much in advance

[Ive J]

One efficient way is to use struct.

myM = struct;
myM.M1 = [myM.M1; newData4M1];
myM.M2 = [myM.M2; newData4M2];

So each field can grow independently. Of course, you can also use cell in a similar way.

[Javier Mateo]

Thank you! That works perfectly.

Now I have the doubt about how to arrange the data by the source. I only know how to do it using if:

if source=="M1"
    myM.M1 = [myM.M1; new_line];
    
    elseif source=="M2"
    myM.M2 = [myM.M2; new_line];
    
    ...
        
    elseif source=="M8"
    myM.M8 = [myM.M8; new_line];
    
end

I have to write only "M8" sources. But what If I have M20 or M100? Is there a proper way to do this, or am I in the correct direction?

[Stephen23]

In the end, will all of the matrices have the same number of rows?

"Is there a proper way to do this, or am I in the correct direction?"

You should replace that IF/ELSEIF construct with dynamic fieldnames:

https://www.mathworks.com/help//matlab/matlab_prog/generate-field-names-from-variables.html

myM.(source) = [myM.(source);new_line];

[Javier Mateo]

No, sometimes we miss some paket from the sources, thereby we do not have a new line every single second on every of them

Edit: Awesome, I did not know about dynamic fieldnames. Thank you!

[J. Alex Lee]

if you need to write to disk and/or there's lots of data, maybe consider using a database instead of holding a matlab variable in memory? I've played around with sqlite using mksqlite with some success.

[Javier Mateo]

What is "a lot of data" when we talk about programming? (sorry.. not my field :D)

In this scenario, we have an struct of 8 fields, each of them can be up to '360x3 double'. Maybe more in the future...

Considering this struct is a global variable, how does it look like?

(I use global variable because this function is called by callback, so I guess there is no other way, is it?)

[Stephen23]

"What is "a lot of data" when we talk about programming?"

I would say "when it gets close to the size of your available memory".

"I use global variable because this function is called by callback, so I guess there is no other way"

Gobal variables are not a reliable or efficient way to pass data between callbacks (or for that matter between any functions). Global variables are avoided by experienced programmers because their usage wastes programming and debugging time.

The recommended approaches are given here:

https://www.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html

https://www.mathworks.com/help/matlab/creating_guis/share-data-across-callbacks-in-app-designer.html

You might find this useful too:

https://www.mathworks.com/matlabcentral/answers/483657-how-to-create-a-gui#answer_394878

[Javier Mateo]

Thank you very much for the recommendations.

I will consider about that if the programm becomes greater. For now it seems to be working flawless with globals.