How to change comma to dott for multiple text files and save the changes in the same text files?

Dear,

I have multiple text files (3 examples are attached) and i like to oppen each and replace all comma ',' with dot '.' then save the changes in the same text file. Any suggestions?

So far i have the following code:

MyFiles=dir('*.txt');  % reading all the text files in working directory
N=length(MyFiles);     % Number of my files (Here i have 3 attached to this question but the code should work for 100's)
for k=1:N               %Here i need to rad each text file in the loop
    data=MyFiles(k);
    tic;                %Perform the replacing of ´,´ with ´.´ 
    data = strrep(data, ',', '.');  
    %% I tried also using this: data = str2double(data); 
    toc;
                        % Now need to save the changes in the text files 
                        % ,I am not sure if this part works either
    FID = fopen(data, 'w');
    fwrite(FID, Data, 'char');
    fclose(FID);
end

I get the following error:

Answer 1

[Walter Roberson]

The below code will write the changed files into a directory, creating it if needed.

projectdir = '.';
outputdir = 'modified';
if ~isdir(outputdir); mkdir(outputdir); end

MyFiles = dir( fullfile(projectdir, '*.txt'));  % reading all the text files in working directory
filenames = fullfile({MyFiles.folder}, {MyFiles.name});

N = length(filenames);     % Number of my files (Here i have 3 attached to this question but the code should work for 100's)
for k=1:N               %Here i need to rad each text file in the loop
    thisfilename = filenames{K};
    data = fileread(thisfilename);

    %replace comma with dot
    mask = data == ',';
    data(mask) = '.';

    % Now need to save the changes in the text files
    [~, basename, ext] = fileparts(thisfilename);
    newfilename = fullfile( outputdir, [basename ext]);
    [FID, msg] = fopen(newfilename, 'w');
    if FID < 0
        error('failed to open file "%s" because "%s"', newfilename, msg);
    end
    fwrite(FID, Data);
    fclose(FID);
end

[Walter Roberson]

Note:

If you were to upgrade to R2019a or later then you could skip all of this, and instead read the data using readmatrix() with the DecimalSeparator option.

[Harr]

Dear Walter,

Thank you very much! It worked and solved the problem perfectly!

Best regards /Harr

Answer 2

[dpb]

Your variable MyFiles is a dir() struct containing the list of files; addressing it does NOT open the file, simply refers to the content of that struct.

Change the to something more like

d=dir('*.txt');         % dir struct containing list of all the text files in working directory
N=numel(d);
for k=1:N
  S=readlines(d(k).name);                   % read as string array
  S=strrep(S,',','.');                      % do the string substitution
  writematrix(S,d(k).name,'QuoteStrings',0) % rewrite the converted file
end

NOTA BENE!!!! The above overwrites the file without any prompt or other safety features -- BE SURE TO BACKUP ALL YOUR FILES FIRST WHILE DEBUGGING!!!!!

BTW, with recent releases of MATLAB, using readmatrix or similar, you can specify the 'DecimalSeparator' named parameter pair value and avoid having to convert the files themselves. With that instead, you could simply write

d=dir('*.txt');
for k=1:numel(d)
  data=readmatrix(d(k).name,'DecimalSeparator',',','NumHeaderLines',1);
  % do whatever with each data set in turn here
  ....
  % before going on to the next ...    
end

[Walter Roberson]

The user cannot use readlines() because they are using R2018b which was earlier than readlines() which needs R2020b.

[Harr]

Dear dpb,

Thank you very much for your answer, i keep it for future R2020b :)

Bet regards/ H