'The variable appears to change size on every loop iteration'

I have been working on a basic procedural data processing program and my code is as follows: (for the error section - Lines 27-62):

function []= Munguia_BIOEFinal()
    user_direct = uigetdir();
    user_direct_files = dir(user_direct);
    addpath(user_direct);
    logFilename  = strcat('Computed_values.csv');
    if(exist(logFilename,'file'))
        delete(logFilename);
    end
    s_no=0;
    rv_max_val='';
    rv_max_val_std='';
    rv_max_val_mean='';
    Sec_data_val='';
    Sec_data_val_std='';
    Sec_data_val_mean='';
    fid_csv           = fopen(logFilename,'w');
    fprintf(fid_csv, '          Date : %s\n', datestr(now) ) ;
    fprintf(fid_csv,'\n\nS_No,File_Name,Mean P_Max,Std P_Max,mean max dP/dt, std max dP/dt, mean min dP/dt, std min dP/dt,15percentage of max dvd\n');
    for idx=1:length(user_direct_files)
        if ~(strcmp(user_direct_files(idx).name,'.') || strcmp(user_direct_files(idx).name,'..'))
            disp(['reading this file ....' user_direct_files(idx).name]);
            fname = user_direct_files(idx).name;
            fid=fopen(fname);
            tline = fgetl(fid);
            tlines = cell(0,1);
            while ischar(tline)
                tlines{end+1,1} = tline;
                tline = fgetl(fid);
            end
            fclose(fid);
            first_data ='';
            sec_data = ''; 
            fa_data = '';
            fa_data_dash = '';
            rv_data = '';
            rv_data_dash = '';
            disp('Reading data from the file......');
            for file_idx=10:length(tlines)
                data_set = split(tlines{file_idx});
                first_data{end+1} = data_set{2};
                sec_data{end+1} = data_set{3};
                fa_data{end+1} = data_set{4};
                fa_data_dash{end+1} =data_set{5};
                 rv_data{end+1} = data_set{6};
                if ~isempty(rv_data_dash)
                    rv_data_dash{end+1} = data_set{7};
                end
            end
            disp('Writing data to an array......')
            rv_data = data_edit(rv_data);
            sec_data = data_edit(sec_data);
            Sec_data_val{end+1} = max(sec_data);
            Sec_data_val_std{end+1} = std(sec_data);
            Sec_data_val_mean{end+1} = mean(sec_data);
            if isnan(rv_data)
              value=1;  
            else
                [value,value_idx] = findpeaks(rv_data);
            end
            rv_max_val{end+1} = max(value);
            rv_max_val_std{end+1} = std(value);
            rv_max_val_mean{end+1} = mean(value);
            s_no=s_no+1;
            fprintf(fid_csv,'%d',s_no);
            fprintf(fid_csv,',"%s"',char(user_direct_files(idx).name));
            fprintf(fid_csv,',"%s"',mean(rv_data));
            fprintf(fid_csv,',"%s"',std(rv_data));
            fprintf(fid_csv,',"%s"',mean(min(rv_data)));
            fprintf(fid_csv,',"%s"',std(min(rv_data)));
            fprintf(fid_csv,',"%s"',mean(value));
            fprintf(fid_csv,',"%s"',std(value));
            disp('Writing data to a csv file......');
            fprintf(fid_csv,',"%s"\n',max(value)*0.15);
            %saveas(gcf,strrep(fname,'.txt','.png'));%save plot
            %close all;
        end
    end
    rmpath(user_direct);
    fclose(fid_csv);
    disp('csv file created successfully......');
end

When I look on my scripts for solutions to the error, it states to change size on every loop iteration. Consider Preallocating for speed. How would I go about fixing this error in particular

Answer 1

[Jan]

Some hints:

• addpath(user_direct); - Append only folders to Matlab's path, which contain M-files. Avoid to include folders containing data files. Use absolute path names instead.
• strcat('Computed_values.csv') - strcat with a single input does nothing expect wasting time.

logFilename  = fullfile(user_direct, 'Computed_values.csv');
if isfile(logFilename)
    delete(logFilename);
end

You can simplify:

            fid=fopen(fname);
            tline = fgetl(fid);
            tlines = cell(0,1);
            while ischar(tline)
                tlines{end+1,1} = tline;
                tline = fgetl(fid);
            end
            fclose(fid);            

to:

tlines = strsplit(fileread(fullfile(user_direct, fname)), newline);

This should fail:

first_data ='';  % first_data is a CHAR vector
for file_idx=10:length(tlines)
    data_set = split(tlines{file_idx});
    first_data{end+1} = data_set{2};  % first_data is a cell string    

Pre-allocate the array with its final size instead:

nCell = length(tlines) - 9;
first_data = cell(1, nCell);
for iCell = 1:nCell
    file_idx = iCell + 9;
    data_set = split(tlines{file_idx});
    first_data{iCell} = data_set{2};

The error has another problem:

    rv_data{end+1} = data_set{6};    

This fails, if data_set has less than 6 elements. Check this using the debugger:

dbstop if error

Enable the debugger. Run the function again. If Matlab stops, check the contents of the array:

disp(data_set)

This will fail also:

fprintf(fid_csv,',"%s"',mean(rv_data))

mean() replies numerical values, but %s expects a char vector or string. This appears multiple times.

In

fprintf(fid_csv,',"%s"',char(user_direct_files(idx).name));

the char() conversion is not needed: user_direct_files(idx).name is a CHAR vector already.