issue when creating and saving file to specific folder

Hello, everyone. I got a small issue when creating a folder and saving files to it.

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    monthStr = num2str(month);
    mkdir(fullfile(folder,'Data',monthStr));
    dataFolder = fullfile(folder,'Data',monthStr);
    dataFolder 
    cd dataFolder ;

-----------------------------------------------------------------

Here I create a folder /Data/monthStr, where monthStr is a variable, for instance, it can be 202106

it is created under /folder/Data and 'dataFolder' shows its path correctly.

However, when I "cd dataFolder", error message says "Cannot CD to .... (Name is nonexistent or not a directory)."

Secondly, I like to save some downloaded file to this folder

--------------------------------------------------------------------

fullURL=['https://polar.ncep.noaa.gov/waves/hindcasts/multi_1/' monthStr '/gribs/multi_1.glo_30m.hs.' monthStr '.grb2';]; 
filename=[dataFolder,'multi_1.glo_30m.hs.' monthStr '.grb2']; 
[f,status]=urlwrite(fullURL,filename);

--------------------------------------------------------------------

However, the file is saved to the "Data" folder, not "Data/monthStr" folder

Any idea to correct the code?

Thank you!

Answer 1

[Rik]

You shouldn't use cd outside of debugging. In general using a full path is a much better idea with better performance.

The cause of the error is that you used the command syntax, which doesn't allow the use of variables. In this case you would have needed to use cd(dataFolder).

For the second issue you forgot to add the filesep, which fullfile would have done automatically for you.

[shukui liu]

Many thanks, Rik!

Regarding the second issue, I don't get you about "forgot to add the filesep". What should I do if I like to write directly the file to "/Data/monthStr"?

[Chunru]

Assume dataFolder is the folder name, [...] is filename, then:

filename=fullfile(dataFolder,['multi_1.glo_30m.hs.' monthStr '.grb2']);  

[shukui liu]

it works like a charm... many many thanks!

[Rik]

Because there is a difference between Windows and Linux/Mac which character separates folders and files. You can automate this like this:

['folder' filesep 'subfolder' filesep 'file']

which is equivalent to this

fullfile('folder','subfolder','file')

[shukui liu]

Noted!

I am very new with Matlab...

The language is very flexible, really like a language, very different from the old style.

Many thanks for the prompt response!

Answer 2

[Chunru]

When dataFolder is a variable, change directory with the following statement:

cd(dataFolder) ;

[shukui liu]

thank you, Chunru!

[Stephen23]

Avoid using CD in code: it is slow (MATLAB rescans the new folder for all MATLAB files and potentially caches them), changes function scope (which makes debugging harder) and is completely unnecessary.

Using absolute/relative filenames is the recommended approach (much more efficient, less buggy).

[shukui liu]

Thanks, Stephen.

I am working based on previous version code, which reads data from ftp server. Now the data has been shifted to web server.

In previous version, there is such a "filesMask" to get the list of the files on ftp server and then assign their name to "files"? That is what I understand.

Currently, I will download these files directly from web server. Then, to get the "files", I need to go to the folder (cd) and then use the original code. I thought this might be the easiest way to update the code.

Actually, I am not very clear with the two expressions

filesMask = ['multi_1.' type '.*.grb2'];

files = f.dir(filesMask);

I shall appreciate much if you can shed some light on it.

        
        ftpSite = 'polar.ncep.noaa.gov';
        ftpPath = ['/pub/history/waves/multi_1/' monthStr '/gribs'];

        % Connect to the FTP site
        f = ftp(ftpSite);
        f.cd(ftpPath);

        % Get the list of relevant *.grb2 files
        filesMask = ['multi_1.' type '.*.grb2'];
        files = f.dir(filesMask);

        % If no matching files found, issue an error
        if isempty(files)
            f.close();  % Close the FTP connection
            url = ['ftp://' ftpSite, ftpPath];
            error('No %s files were found in <a href="%s">%s/</a>', filesMask, url, url)
        end

        % If fields were specified, then exclude the irrelevant files
        if ~isempty(fields)
            regex = ['\.(' fieldsRegex ')\.'];
            invalidIdx = cellfun('isempty', regexp({files.name},regex));
            files(invalidIdx) = [];
        end

        % Download all files into the Data folder
        if ~exist(dataFolder,'dir')
            fprintf('Downloading %d files into %s ...\n', length(files), dataFolder);
        end