Error using 'Save' including quotation marks around variables

I am running a piece of code that generates and plots two variables (Dmed and DSEM). The code has been used by my workplace for a long time, and it works well. I did not write it.

I want the raw numbers from the plot to save into a .csv file so I can run a separate analysis later looking at the individual numbers generated.

This is a loop that runs through selected data.

Every time I try to run it, it returns the same error:

Error using save

Must be a string scalar or character vector.

save([filename, '_output', '.csv'], 'Dmed', 'DSEM')
% I have also tried this without 'Dmed' and 'DSEM', where the variables are run like this:
save([filename, '_output'], Dmed, DSEM)

Answer 1

[madhan ravi]

Use writematrix() or dlmwrite() or csvwrite() for older versions bearing in mind that

 filename = 'sample'; % for example

[Nora Laine Herzog]

It is not an old version. I am using MATLAB_R2020a. Filename was defined earlier in the code, and I don't have difficulties, except when I am trying to save the variables. If I am running the full code, which plots the variables that I want to save, I get no errors. That is why I am confused.

Answer 2

[Steven Lord]

My guess is filename is a cell array containing a char row vector.

x = 1:10;
thefile = 'data571924.mat';
save(thefile, 'x') % works

thefile2 = {'data571924_cell.mat'};
save(thefile2, 'x') % fails

save(char(thefile2), 'x') % works

Many functions that can accept a char vector can also accept a cell array containing a char vector. save is not one of those many functions.