Load multiple variables into single excel file

Hi, I have multiple .mat files which all contain 31 variables (1 for each day of the month) the variables are all 21600x5 tables.

I can loop through different .mat files:

files = what('Extract_parameter'); %list all the mat.files in the folder
for i = 1:length(files.mat)
i;
GenNum = files.mat{i}; %generator mat file
load (['Extract_parameter\' GenNum]); %load each file in the folder
end

and I am familiar with the writetable function:

writetable(T,'myfile.xlsx')

where I am stuck is looping through all the 31 variables in the .mat file and export it to one single table. That is I want one excel file which contains all the data from one .mat file (all 31 variables)

[Stephen23]

The trick is to load into a variable (which is a structure):

S = load(...);

Once you have one structure S you can loop over its fieldnames, or perform operations on the whole structure.

Note: anytime that you find yourself trying to access lots of separate variables you are doing something wrong: keep data together as much as possible, because this makes processing it much simpler. One of the most important ways of achieving this is to load into an output variable, rather than simply spamming all of the variables in the .mat file directly into the workspace. Read this to know more:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Answer 1

[Ameer Hamza]

You can refer to my answer to your other question to see how can you combine multiple tables into one. Now for this question, as far I understand, each mat file contains 31 tables and you have several mat files and you want to generate 1 excel file corresponding to each mat file. As suggested by @Stephen, it is better to load mat file into a struct to avoid any confusion. Your given code can be modified as follow

files = what('Extract_parameter'); %list all the mat.files in the folder
for i = 1:length(files.mat)
  GenNum = files.mat{i}; %generator mat file
  big_table = [];
  tables = load (['Extract_parameter\' GenNum]); %load mat file into struct.
  f = fieldnames(tables)';
  for j=f
    % here I am assuming that tables struct only contain tables class variables. Otherwise, you might want to add if class(tables.(j{:})) == "table" before next statement
    big_table = [big_table; tables.(j{:}){:,:}]
  end
  big_table = cell2table(big_table);
  writetable(big_table, ['myfile' num2str(i) '.xlsx']);
end

The above method will work even if all tables have different column names. This script will generate 'myfile1.xlsx', 'myfile2.xlsx', ... and so on, upto the number of mat files.

[Stephen23]

@Ameer Hamza Khan: given that i is a scalar cell containing a char vector, what does this do?:

num2str(i)

How did you test this code?

[Ameer Hamza]

I pasted my code inside's OP's code and therefore the mistake happened. I have fixed it now.

[Karina]

Ameer, yes that is correct I have over 300 mat files (all of which have 31 variables) and I want one excel file for ever mat file. Your code makes perfect sense except the last part:

 writetable(big_table,['myfile' num2str(i) '.xlsx']);   % code
  end

what does i refer to here? because I get an error saying i must be numeric.

[Ameer Hamza]

There was a mistake in my original answer, as pointed out by @Stephen. I made an edit to the posted code. You might be using the older version. Can you check if inner for loop have j=f instead of i=f. Also, it is a better MATLAB coding practice to use ii and avoid i as a variable name, as it already represents imaginary number iota and will cause errors if used carelessly.

[renata delocco villa coutinho]

what happends if I don't have tables with the same syze and I want to have at the end 1 .mat instead of .xlsx files? can you help me to improve the code?