read newest file in loop

Hi, I've been working on matlab trying to make a while loop that would read the newest file from a live feed directory, and would stop when there are no new files available.

The whole code is quite big, so I won't post it, but I believe the main problem is this piece here:

            dir1=fileList;
            [~,dx] = sort([dir1.datenum],'descend');
            newest = dir1(dx(end)).name; % returns newest file

which works perfect by itself, but when used more than once it returns the error:

"Dot name reference on non-scalar structure." on "[~,dx] = sort([dir1.datenum],'descend');"

Also tried using

       d1 = fileList;
       dates = [d1.datenum];
       [~, newestIndex] = max (dates);
       d1(newestIndex);
       d1.date % will display long list of files and stuff, consider deleting...
       newest = d1(newestIndex(end)).name;

returns same error.

I've also tried using just the last line i.e.

      newest = dir1(dx(end)).name; % returns newest file

But does not seem to refresh the dir in question.

To clarify: - code will check for the newest file available (image) - after process, refresh and check for newest file again, use strcmp to compare filenames and see if new file exists.

- if it does --> loop: run as long as new files arrive.

Hope its more clear now...

Currently, does not appear to discover any newer files than the first instance.. so it doesn't even reach the loop.

Any help is appreciated!

Answer 1

[Walter Roberson]

You are overwriting FileList with something that is not the result of dir() . For example you might be assigning to it a list of file names at some point.

[t33dot]

Hey thanks for the reply, I looked into what you said but i'm still clueless. Thought I should give more info on this:

fileList is being used as a function to exclude bad/hidden files,

       fileList = getAllFiles(feed);

which expands to:

function fileList = getAllFiles(dirName)

    fileList = dir(dirName);

    %# the first two entries in fileList are current and parent dir
    %# so we'll ignore them
    fileList(1:2) = [];

    %# remove all folders
    isBadFile = cat(1,fileList.isdir); %# all directories are bad

    %# loop to identify hidden files
    for iFile = find(~isBadFile)' %'# loop only non-dirs
        %# on OSX, hidden files start with a dot
        isBadFile(iFile) = strcmp(fileList(iFile).name(1),'.');
        if ~isBadFile(iFile) && ispc
            %# check for hidden Windows files - only works on Windows
            [~,stats] = fileattrib(fullfile(dirName,fileList(iFile).name));
            if stats.hidden
                isBadFile(iFile) = true;
            end
        end
    end

    %# remove bad files
    fileList(isBadFile) = [];

end

Typing in fileList in matlab results:

209x1 struct array with fields:
  name
  date
  bytes
  isdir
  datenum

meant to be a modified dir (?)

and finally, using this

fileList = getAllFiles(feed);
       d1 = fileList;
       dates = [d1.datenum];
       [~, newestIndex] = max (dates);
       d1(newestIndex);
       newest = d1(newestIndex(end)).name; %Returns name of newest file.

'newest' results in the newest filename from the chosen dir. But I can't seem to structure it in a way where it can be used again later in the code, in order to check for a new file again, and hence compare the two. It gives me that dot name ref error. tried renaming every variable but doesn't seem to help.

How would you approach this?

p.s. sorry for the long post...

[Walter Roberson]

Are you calling getAllFiles() to refresh the list?

Is your "feed" variable an absolute path or a relative path? If it is a relative path, then is there anything in your code that changes directory? If there is then possibly the dir() is returning an error instead of a list of files.

Note: you do not need to exclude . and .. specifically with your code, and it is safer not to. The isdir flag will be set for them.

[t33dot]

im sorry, getallfiles () is wrongly named its actually used to remove the hidden or bad files, the . and ..

when I don't use it, 'newest' always returns .. instead of an actual file

'feed' is the absolute path, i.e. feed = 'D:\Pictures\...', and it remains the same throughout.

Tried clear variables:

            clear('fileList','dates','d1','d2','datenum','newestIndex','fileList2');

       fileList = getAllFiles(feed);        
       d2 = fileList;
       dates = [d2.datenum];
       [~, newestIndex2] = max (dates);
       d2(newestIndex2);
       newest2 = d2(newestIndex2(end)).name; %Returns name of newest file.
       save()

And get the same thing:

Dot name reference on non-scalar structure.

Error in improcc (line 205)

         dates = [d2.datenum];

[t33dot]

Good news! so I embedded this into a function, and use that instead. No more error! and loop works now. A joyous occasion :D. Seemed like a matlab bug to me...

I appreciate your help on this! Thanks again.