Output new column to existing csv file with multiple columns

I have hundreds of csv files for which I'm running a function to shuffle the data in the 6th column and I need to output this shuffled data to a new column inside the existing file. All of the files currently have 6 columns so I need the shuffled data to be the 7th column. The csv files vary in length but all columns within the same file are the same length.

I tried using the code from this question: https://au.mathworks.com/matlabcentral/answers/23723-add-new-column-into-existing-text-file

but I dont understand where to include the new column of data. Also it is from 2011 so perhaps there is an easier solution?

Thank you.

Here is a preview of one of the files:

      Unnamed: 0 x y z unixTime mag
    0 14272 -0.546875 1.484375 -0.1875 1506448016 1.5929838844916167
    1 14273 -0.59375 1.25 -0.21875 1506448016 1.4010319857162434
    2 14274 -0.40625 0.90625 -0.03125 1506448016 0.9936320684740404
    3 14275 -0.296875 0.78125 0.046875 1506448016 0.8370684522486797
    4 14276 -0.171875 0.671875 0.15625 1506448016 0.7108945728798328
    5 14277 -0.140625 0.65625 0.1875 1506448016 0.6968469725305549
    6 14278 -0.21875 0.578125 0.046875 1506448016 0.6199010757774179

I've been using dlmread to cut off the first row of strings (col headers) when I load in the data. Not sure why the values are shifted in the preview

[Ameer Hamza]

What is your file type? txt, csv, mat, ...?

[Centauri Jolene]

csv, ill edit to include in the question, thanks

[Walter Roberson]

Please show the first few lines of one of your files.

[Centauri Jolene]

Sure, Not sure why the values are shifted in my preview

Answer 1

[Walter Roberson]

t = readtable('YourFile.csv');

t.newmag = t.mag(randperm(height(t)));     %shuffled version of column 6

%any header that was not a valid variable name was modified and the original put
%into VariableDescriptions
hdr = t.Properties.VariableNames;
orig_hdr = t.Properties.VariableDescriptions;
mask = ~cellfun(@isempty, orig_hdr);
hdr(mask) = orig_hdr(mask);

hdr_str = strjoin(hdr, ',');
fid = fopen('NewFile.csv', 'wt');
fprintf(fid, '%s\n', hdr_str);
fprintf(fid, '%d,%d,%g,%g,%g,%g\n', t{:,:}.');  %relies on data being pure numeric
fclose(fid)

Answer 2

[Ameer Hamza]

Adding a column to a csv file is not as trivial as adding new rows. You will need to read complete file, change the data in MATLAB workspace and the re-write data to the csv file. Here is a general sketch of the code

data = csvread(filename);
% do processing on data, in your case shuffle 6th column and write it to 7th column of matrix
csvwrite(filename, changedData);