Subscripted assignment between dissimilar structures and Error: The variable info in a parfor cannot be classified. I need educating!

I am having difficulty trying to speed up code by using parfor and pre-defining variable dimensions. The original code looks something like this(abbreviated):

for i = 1 : num_files_in_folder
    Flag = true;
    foldername = files_in_folder(i).name;
    try
        info = dicominfo(foldername);
    catch ME
        Flag = false;
        warning("Problem: dicominfo error.");
        DB2(i,1) = "Bad DICOM File";
        DB2(i,2) = foldername;
%         rethrow(ME);
    end  %%try
...

When trying to speed it up with parfor I get the "cannot be classified" and other similar error messages.

Then I tried moving some of these temporary variables outside and making them an structured array. Note: I have ram to spare, even with a 8G ram disk. So big variable are not an issue yet.

[Matt J]

I get the "cannot be classified" and other similar error messages.

Post them in their entirety please. Also post the complete loop. Do the messages reference any of the variables you've shown above? I can't see anything wrong with that code snippet.

[Stephen23]

Patrick Ford's "Answer" moved here:

OK, Matt - just trying to keep the text volume low. As an explanation: move_Dicom.m is the part I was attempting to improve with parfor.

DicomReadMatout.m is the full program - still need work writing out.

pfortestd.m is code I was trying to use to debug.

string2hash.m is a function called.

Thank you for the interest.

Answer 1

[Walter Roberson]

Here is a marginally cleaned up version that does not have the parfor errors, and which manages directories a little better. Untested.

You should double-check the line

          ExamsInfo(i,:) = [{infx(i)},{thisfile}];

I do not understand why you would not use

          ExamsInfo(i,:) = {infx(i), thisfile};

%clear
% Script to extract a specified Dicom series from the PET/CT data set

WarmFuzzy = 0;
data_folder = uigetdir;
files_in_folder = dir( fullfile(data_folder, '*.dcm'));
% Discard the current and root file descriptors
files_in_folder = files_in_folder( [files_in_folder.bytes] > 0);
filenames_in_folder = fullfile(data_folder, {files_in_folder.name});

      num_files_in_folder =  numel(filenamess_in_folder);
      DB2 = strings([num_files_in_folder,2]);

      dlu = dicomlookup('0008', '103E');

% I searched for a series descriptor called �docs�; You can change it to what you need.
% desired_series_descriptor = 'docs';

ExamsInfo = cell(num_files_in_folder,2);
Flag(1:num_files_in_folder) = true;
Flag1(1:num_files_in_folder) = true;

n = num_files_in_folder;
infx(1:10) = dicominfo(filenames_in_folder{1});

for i = 1:num_files_in_folder
    infx(i) =  dicominfo(filenames_in_folder{i});
    str1(i) = infx(i).(dlu);
end

% foldername(1:num_files_in_folder) = ' ';

parfor i = 1 : num_files_in_folder
    newDB2 = strings(1,2);
    thisfile = filenames_in_folder{i};
    try
        infx(i) = dicominfo(thisfile);
    catch ME
        Flag(i) = false;
        warning("Problem: dicominfo error.");
        newDB2(1) = "Bad DICOM File";
        newDB2(2) = thisfile;
%         rethrow(ME);
    end  %%try
    if (Flag(i))
        Flag1(i) = true;
       try
           str1(i) = infx(i).(dlu);
       catch ME
           warning("No Series Discription");
           newDB2(1) = "Nyet";
           newDB2(2) = thisfile;
           Flag1(i) = false;
       end  %%try

          if(Flag1(i))
              newDB2(1) = str1(i);
              newDB2(2) = thisfile;
          end  %% if(Flag1)

       % You can convert this section to a series of if statements to match multiple descriptors
       % and get the file names for the specific files that you are interested in, and then read the data in
       % using DICOM read

          ExamsInfo(i,:) = [{infx(i)},{thisfile}];
      end % if Flag

      DB2(i,:) = newDB2;
  %    WarmFuzzy = WarmFuzzy +1;
  %     xt = sprintf('%d Interation\n', WarmFuzzy);
  %     disp(xt);
  end %%parfor i = 1 : num_files_in_folder

    disp("Done  reading in the directory information");
  %  parsing the information - creating the database

Dicom_type = {'[GA-N_CTAC_60s] Rest Rb' '[NG_NAC_60s] Stress Rb' 'Cardiac-ldCT' '[NG_NAC_60s] Rest Rb' '[NG_CTAC_60s] Rest Rb' '[NG_CTAC_60s] Stress Rb' '[GA-N_CTAC_60s] Stress Rb'};

% N = size(DB2);
prime = 1033; %  61;
LTA = strings(prime,361);
ptr_lga(prime,361) = int16(0);
%   test debug  number double due to second run?
    for i = 1:prime
        ptr_lga(1,1) = 0;
    end

nitem(1:prime) = int16(1);

hflag = true;

for i= 1:num_files_in_folder
    Logical_Flag =  (DB2(i,1) ~= "Bad DICOM File") && (DB2(i,1) ~= "Nyet") ...
                    && convertCharsToStrings((ExamsInfo{i, 1}.AccessionNumber) ...
                    == convertCharsToStrings(ExamsInfo{1, 1}.AccessionNumber));

      if (Logical_Flag)
      if (hflag)
          arr = convertStringsToChars(DB2(i,1));
          hash = mod(string2hash(arr), prime)+1;
      end  %%if (hflag)
      hflag = true;

      switch LTA(hash,1)
          case ""
              LTA(hash,1)= DB2(i,1);
              nitem(hash) = nitem(hash) + 1;
              LTA(hash,nitem(hash)) = DB2(i,2);

%           test if this is an image we need
            lg2 = false;
            lg = ( DB2(i,1) == Dicom_type);

              for j = 1:7
                  lg2 = lg2 | lg(j);
              end

              if lg2
                  ptr_lga(hash,nitem(hash)) = int16(ExamsInfo{i,1}.InstanceNumber);
                  ptr_lga(hash,1) = ptr_lga(hash,1) +1;
              end

          case DB2(i,1)
              nitem(hash) = nitem(hash) + 1;
              LTA(hash,nitem(hash)) = DB2(i,2);
              %           test if this is an image we need
              lg2 = false;
              lg = ( DB2(i,1) == Dicom_type);

              for j = 1:7
                  lg2 = lg2 | lg(j);
              end

              if lg2
                  ptr_lga(hash,nitem(hash)) = int16(ExamsInfo{i,1}.InstanceNumber);
                  ptr_lga(hash,1) = ptr_lga(hash,1) +1;
              end

          otherwise
              if ~(LTA(hash,1) == DB2(i,1))
                  hflag = false;
                  i = i-1;
                  hash = mod((hash+7),prime);
              else                
                  error('Unexpected event - Halting execution');
              end  % if ~(LTA(hash,1) == DB2(i,1))
      end  %  switch LTA 
      end  % if num_files_in_folder
  end

Dicom_name = {"Rest_gated_AC" "StressNG_NAC" "Cardiac_CT" "Rest_NG_NAC" "Rest_NG_AC" "Stress_NG_AC" "Stress_gated_AC"};

exit;
hashtag(1:7) = int16(0);
Rand_Num_Name = string( int16(rand(1,1) * 50000));

for i=1:7
hashtag(i) = mod(string2hash(char(Dicom_type(i))), prime)+1;
      while (Dicom_type(i) ~= LTA(hashtag(i)))
        hashtag(i) = mod((hashtag(i)+7),prime);
      end   % while
      slicex = dicomread(LTA(hashtag(i),2));
      num_slices = ptr_lga(hashtag(i),1);
      [x,y] = size(slicex);
      Dimage = int16(zeros(num_slices,x,y));

        for k = 1:num_slices
            indx = ptr_lga(hashtag(i),(k+1));
            Dimage(indx, 1:x,1:y) = dicomread(LTA(hashtag(i),(k+1)));
        end
        % Now write the file out
        save(strcat(string(Dicom_name(i)),"_", Rand_Num_Name, ".mat"), 'Dimage')

end
IDt.PatientName = ExamsInfo{1, 1}.PatientName;
IDt.AccessionNumber = ExamsInfo{1, 1}.AccessionNumber;
IDt.StudyDate = ExamsInfo{1, 1}.StudyDate;

save(char(strcat("IDt", Rand_Num_Name, ".mat")), 'IDt')