Storing x and y data calculated in loop as arrays to be used in the creation of a table.

Hello. I am currently taking data during a loop (changing an outside variable M with each loop). This data is in the form of two arrays of length N. As of now my code plots these arrays and then goes on to the next loop, overwriting the arrays. I am wondering how I might store these values, to create a table something like this, adding columns x and y for each M(iteration). I would then try to export it to a csv/excel, but that's later I suppose lol.

I tried to create an empty array of zeros(N, 2*M) and then assign the x and y of each iteration to the i and i+1 (odds and even) respectively, but that wasn't fruitful. Do you folks have any other ideas as to what I might do?

Answer 1

[Walter Roberson]

M = table();

for K = 1 : 3
    X = randi(9, 5, 1); Y = randi(9, 5, 1);
    thisM = table(X, Y);
    M = addvars(M, thisM, 'NewVariableNames', "M" + K);
end

M

M = 5×3 table
      M1        M2        M3  
    X    Y    X    Y    X    Y
    ______    ______    ______

    8    6    5    4    4    4
    9    1    6    2    1    9
    6    1    1    9    7    5
    6    9    9    7    6    4
    6    5    3    6    2    9

M_to_write = splitvars(M);
writetable(M_to_write, 'YourFile.csv')

dbtype YourFile.csv

1     M1_X,M1_Y,M2_X,M2_Y,M3_X,M3_Y
2     8,6,5,4,4,4
3     9,1,6,2,1,9
4     6,1,1,9,7,5
5     6,9,9,7,6,4
6     6,5,3,6,2,9

If you need the headers M1 M2 M3 in the file, then you have questions about what columns to write them into.

For text files you can write a header into a file using any of several text-writing functions, and then you can writetable() with 'writemode', 'append' . Or, you can split your table into cells and add a header cell and use writecell()

[Dametre]

That makes so much sense. I'm rather new to MATLAB (Python experience), So seeing this laid out it looks like you're using the iterator to add a unique dataset of x,y, which doesn't cause an overwrite/duplicate name. I really appreciate your time, It is very helpful for me to see the code written out in such a way. I don't think I need the headers in the file, I may end up attempting to do so to help me learn more, but I believe I can just index numerically in this application :)

Thank you so much!

[Walter Roberson]

The key to my code is that you can put a table() object inside a table() object, and if you do then it displays nicely. But unfortunately writetable() cannot handle writing the multiple levels of headers.

Answer 2

[Oguz Kaan Hancioglu]

You can use table data object in matlab.

Best

x = 1:4';
y = 1:4';
M1 = table(x,y)

M1 = 1×2 table
           x                   y        
    ________________    ________________

    1    2    3    4    1    2    3    4

M2 = table(x,y)

M2 = 1×2 table
           x                   y        
    ________________    ________________

    1    2    3    4    1    2    3    4

M3 = table(x,y)

M3 = 1×2 table
           x                   y        
    ________________    ________________

    1    2    3    4    1    2    3    4

T = table(M1,M2,M3)

T = 1×3 table
                     M1                                      M2                                      M3                 
           x                   y                   x                   y                   x                   y        
    ____________________________________    ____________________________________    ____________________________________

    1    2    3    4    1    2    3    4    1    2    3    4    1    2    3    4    1    2    3    4    1    2    3    4