How to add headers to an array and output to a text file?

I have an array of numbers of type double. Each row is of length 3xN where N is some fixed number. I want to reshape each row as a sub-array of length N x 3 with the header THIS IS SUB-ARRAY: x, where x is the number of the sub-array. Finally, I want to output as a text file. For example, the given data (attached) I want to have:

THIS IS SUB-ARRAY: 1

0.814723686393179 0.913375856139019 0.278498218867048

0.964888535199277 0.957166948242946 0.141886338627215

0.792207329559554 0.0357116785741896 0.678735154857774

THIS IS SUB-ARRAY: 2

0.905791937075619 0.632359246225410 0.546881519204984

0.157613081677548 0.485375648722841 0.421761282626275

0.959492426392903 0.849129305868777 0.757740130578333

THIS IS SUB-ARRAY: 3

0.126986816293506 0.0975404049994095 0.957506835434298

0.970592781760616 0.800280468888800 0.915735525189067

0.655740699156587 0.933993247757551 0.743132468124916

I think I can do the reshaping of each row by something like

[nrow,ncol] = size(x);
for i = 1:nrow
    A = x(i,:);
    B = reshape(A, [ncol,3]);
end

But how do I add the header and output to a text file?

Answer 1

[Walter Roberson]

One way:

Put the various values into a cell array, and then writecell()

Another way:

Construct a string array from the various lines, and then writelines()

Third way: fopen(), loop using fprintf() to write header and contents; afterwards fclose()