ARFF reader/writer for MATLAB -- http://decabyte.it/projects/arff-reader-writer-for-matlab/

arff_read.m

% ARFF_READ - Read content of an ARFF file to a MATLAB's struct array.
%
%   [DATA, relname, nomspec] = ARFF_READ(arff_file)
%       arff_file => input file (.arff / .arff.gz extension)
%       relname => relation name (string)
%       DATA => struct array representing data and attributes (n x attrs)
%       nomspec => struct array defining nominal-specification attributes
%
%   NOTES:
%       See ARFF_WRITE to read notes about relname and nomspec.
%       See ARFF format specification on WEKA site.

function [data, relname, nomspec] = arff_read(arff_file)

    if nargin < 1
        error('MATLAB:input','Not enough inputs!');
    end
    
    if isempty(arff_file)
        error('MATLAB:input','Bad file name!');
    end
    
    % check file extention
    [~, ~, ext] = fileparts(arff_file);
    
    if strcmpi(ext,'.arff')
        
        % open file
        fid = fopen(arff_file, 'r+t');
        
    elseif strcmpi(ext,'.gz')
        
        % temporary working dir
        outdir = tempdir;
        
        % decompress
        dec_files = gunzip(arff_file, outdir);
        
        if ~isempty(dec_files)
            fid = fopen(dec_files{1}, 'r+t');
        else
            error('%s is not a valid arff_file', arff_file);
        end            
    
    else
        error('%s is not a valid arff_file', arff_file);
    end    
    
    if fid == -1
        error('MATLAB:file','File not found!');
    end  
    
    % read relname
    relname = [];
    
    while isempty(relname)
        tline = fgetl(fid);
        
        if ~ischar(tline)
            fclose(fid);
            error('MATLAB:file','ARFF file not recognized!');
        end
        
        % avoid parsing @DATA and skip blank lines
        if length(tline) > 9 && tline(1) == '@' && strcmpi(tline(2:9),'RELATION')
            relname = tline(11:end);
            break;
        end            
    end
    
    % read attributes
    fields = {};
    ftypes = [];
    
    floop = 1;
    fn = 1;
    
    while floop
        tline = fgetl(fid);
        
        if ~ischar(tline)
            break;
        end
        
        % avoid parsing @DATA and skip blank lines
        if length(tline) > 5 && tline(1) == '@' && strcmpi(tline(2:10),'ATTRIBUTE')
            
            %at = strfind(tline, ' ');
            %
            %if length(at) < 2
            %    error('MATLAB:file','ARFF file not recognized!');
            %end
            %
            %fields{fn} = tline(at(1)+1:at(2)-1);
            %typedef = tline(at(2)+1:end);
            
            % parsing using textscan? (good for data, less for attributes)
            A = textscan(tline,'%s %s %s','Whitespace',' \t\b{},');
            
            if isempty(A{1}) || isempty(A{2}) || isempty(A{3})
                fclose(fid);
                error('MATLAB:file','ARFF file not recognized!');               
            end
            
            if size(A{1},1) == 1
                fields{fn} = char(A{2});
                typedef = char(A{3});
            else
                fields{fn} = char(A{2}(1));
                bt = strfind(tline,'{');
                typedef = tline(bt(1):end);
            end
            
            if typedef(1) == '{' && typedef(end) == '}'
                ftypes(fn) = 1;
                %nomspec.(fields{fn}) = typedef;
                
                % out is a cell with parsed classes assuming { x, x, x } format  
                out = textscan(typedef, '%s', 'Delimiter', ' ,{}', 'MultipleDelimsAsOne', 1);
                
                % expand cell (avoid cell of cell)
                nomspec.(fields{fn}) = out{:};
            else
               if strcmpi(typedef,'NUMERIC')
                   ftypes(fn) = 0;
               elseif strcmpi(typedef,'STRING')
                   ftypes(fn) = 2;
               else 
                   dt = strfind(typedef, ' ');
                   
                   if ~isempty(dt) && strcmpi(typedef(1:dt(1)-1), 'DATE')
                       ftypes(fn) = 3;
                       % implement date-format parsing
                   else
                       fclose(fid);
                       error('MATLAB:file','ARFF file not recognized!');
                   end
               end
            end
            
            fn = fn + 1;
        end
        
    end
    
    % create data struct
    data = struct();
    
    for fn = 1 : length(fields)
        data.(fields{fn}) = [];
    end
    
    % store empty struct
    data_tmpl = data;
       
    % rewind file
    fseek(fid,0,-1);
        
    % seek data
    has_data = 0;
    
    while floop
        tline = fgetl(fid);
        
        if length(tline) == 5 && strcmpi(tline(1:5),'@DATA')
            has_data = 1;
            break;
        end
        
        if ~ischar(tline)
            break;
        end
    end
    
    if has_data == 1
        
        dcnt = 1;
        
        while floop
            tline = fgetl(fid);

            if length(tline) > 1
                
                % find values
                vt = strfind(tline,',');
                
                % init with empty struct
                data(dcnt) = data_tmpl;
                
                for k = 1 : length(vt) + 1
                
                    if k == 1
                        if isempty(vt)
                            content = tline(1:end);
                        else
                            content = tline(1:vt(k)-1);
                        end
                    elseif k <= length(vt)
                        content = tline(vt(k-1)+1:vt(k)-1);
                    else
                        content = tline(vt(k-1)+1:end);
                    end

                    switch ftypes(k) 
                        case 0
                            data(dcnt).(fields{k}) = str2double( content ); %str2num( content );
                        case 3
                            data(dcnt).(fields{k}) = datenum( content(2:end-1), 'yyyy-mm-dd HH:MM:SS' );
                        otherwise
                            data(dcnt).(fields{k}) = content;
                    end
                
                end
                
                dcnt = dcnt + 1;
                
            end

            if ~ischar(tline)
                break;
            end
        end
        
    end
    
    % close file
    fclose(fid);
    
    % remove temporary decompressed file
    if exist('dec_files','var') && ~isempty(dec_files)
        delete(dec_files{1});
    end

end

% References:
%   [1]: http://www.cs.waikato.ac.nz/ml/weka/arff.html

arff_write.m

% ARFF_WRITE - Saves a MATLAB's struct array to file using ARFF file format.
%
%   ARFF_WRITE(arff_file, DATA, relname, nomspec)
%       arff_file => output file (.arff / .arff.gz extension)
%       DATA => struct array representing data and attributes (n x attrs)
%       relname => relation name (string)
%       nomspec => struct array defining nominal-specification attributes
%
%   NOTES:
%       Attribute name is taken from DATA struct fieldname and attribute
%       type is taken from field data-type.
%
%       Append "_class" to a DATA struct fieldname to save an attribute as
%       nominal-specification attribute and specify the nominal-names
%       inside NOMSPEC struct array using as fieldname the DATA struct's
%       fieldname and as content a cell array of names (string).
%
%       Append "_date" to a DATA struct fieldname and use numerical date
%       representation (using datenum) to save an attribute as date type 
%       (using 'yyyy-mm-dd HH:MM:SS' format in ARFF file).
%
%       TODO -- According to SPEC any attribute that contain space must be 
%       quoted using single quote char.
%
%       See ARFF format specification on WEKA site.

function [] = arff_write(arff_file, data, relname, nomspec)

    if nargin < 3
        error('MATLAB:input','Not enough inputs!');
    end
    
    if isempty(data) || ~isstruct(data)
        error('MATLAB:input','Please use struct data input!');
    end
    
    if isempty(arff_file)
        arff_file = sprintf('output-%d.arff', randi(1000,1));
    end
    
    if isempty(relname)
        relname = sprintf('relname-%d', randi(1000,1));
    end
    
    % check file extention
    [arff_path, arff_name, ext] = fileparts(arff_file);
    
    if strcmpi(ext,'.arff')
        
        % open file
        fid = fopen(arff_file, 'w+t');
        
    elseif strcmpi(ext,'.gz')
        
        % temp file
        outfile = fullfile(tempdir, arff_name);
        
        % open file
        fid = fopen(outfile, 'w+t');
    
    else
        error('%s is not a valid arff_file', arff_file);
    end
    
    % write relname
    fprintf(fid, '@RELATION %s\n\n', relname);
    
    % write attributes
    fields = fieldnames(data);
    ftypes = zeros(size(fields));
    
    for fn = 1 : length(fields)
        
        if isnumeric( data(1).(fields{fn}) )
            
            dt = strfind(fields{fn}, '_date');
            
            if isempty(dt)
                type = 'NUMERIC';
                ftypes(fn) = 0;
            else
                % check SimpleDateFormat (java.doc) to accept this instead of ISO-8601
                type = 'DATE "yyyy-mm-dd HH:MM:SS"';
                ftypes(fn) = 3;
                %name = fields{fn}(1:max(dt)-1);
            end
            
        elseif ischar( data(1).(fields{fn}) )
            
            ct = strfind(fields{fn}, '_class');
            
            if isempty(ct)
                type = 'STRING';
                ftypes(fn) = 2;
            else           
                if isstruct(nomspec) && isfield(nomspec, fields{fn}) && ...
                        iscell(nomspec.(fields{fn}))
                    
                    type = '{';

                    for k = 1 : length( nomspec.(fields{fn}) ) - 1
                        type = sprintf( '%s %s,', type, nomspec.(fields{fn}){k} );
                    end

                    type = sprintf('%s %s }', type, nomspec.(fields{fn}){k+1});

                else
                    fclose(fid);
                    error('MATLAB:input','Inferring class specification from data!');
                    % TODO inference
                end
                
                ftypes(fn) = 1;
                %name = fields{fn}(1:max(ct)-1);
            end
            
        else
            fclose(fid);
            error('MATLAB:input','Cannot convert %s field to ARFF format!', fields{fn});
        end
        
        fprintf(fid, '@ATTRIBUTE %s %s\n', fields{fn}, type);
        %fprintf(fid, '@ATTRIBUTE %s %s\n', name, type);
        
    end
    
    % write data
    fprintf(fid, '\n@DATA\n');
    content = '';
    
    for n = 1 : length(data)
       
        for fn = 1 : length(fields)
            
            if isempty(data(n).(fields{fn}))
                content = '?';
            else
                switch ftypes(fn)
                    case 0
                        content = num2str( data(n).(fields{fn}) );
                    case 1
                        content = data(n).(fields{fn});
                    case 2
                        content = data(n).(fields{fn});
                    case 3
                        content = ['"' datestr(data(n).(fields{fn}), 'yyyy-mm-dd HH:MM:SS') '"'];
                end
            end
            
            if fn < length(fields)
                fprintf(fid,'%s,', content);
            else
                fprintf(fid,'%s', content);
            end
            
        end
        
        fprintf(fid,'\n');
        
    end
    
    % close file
    fclose(fid);
    
    % remove temporary file & compress .arff
    if exist('outfile','var') && ~isempty(outfile)
        gzip(outfile, arff_path);
        delete(outfile);
    end

end

% References:
%   [1]: http://www.cs.waikato.ac.nz/ml/weka/arff.html

example_read.m

% example_read.m

clear all; close all; clc;

path(path, '..');

%% import dataset
infile = 'example_dataset.arff';

% load arff
[data, relname, nomspec] = arff_read(infile);

% extract nominal specification attribute
type_class = nomspec.type_class;

%% plot dataset
plot([data.idx], [data.high], 'r.-'); grid on; hold on;
plot([data.idx], [data.med], 'g.-'); grid on; hold on;
plot([data.idx], [data.low], 'b.-'); grid on; hold on;

m_values = mean([ data.high; data.med; data.low ]');

for k = 1 : length(m_values)
    hr = refline(0, m_values(k));
    set(hr,'Color','k','LineStyle','--');
end

legend('high','med','low');

tl = title(relname);
xl = xlabel('idx');
yl = ylabel('value');
set(tl,'Interpreter','none');

set(tl,'FontSize', 14); 
set(xl,'FontSize', 12); 
set(yl,'FontSize', 12);

%% type histogram
T = {data.type_class};
[B,I,J] = unique(T);

f = figure();
hist(J,length(B)); grid on;
xlim([0.5 3.5]);

hp = findobj(f,'Type','patch');
set(hp,'FaceColor','r','EdgeColor','w');

% labels
[n,x] = hist(J,length(B));
text(x, n, type_class, 'horizontalalignment', ...
    'center', 'verticalalignment', 'bottom');

tl = title(relname);
xl = xlabel('class');
yl = ylabel('count');
set(tl,'Interpreter','none');

set(gca,'XTick',[]);
set(tl,'FontSize', 14); 
set(xl,'FontSize', 12); 
set(yl,'FontSize', 12);

example_write.m

% example_write.m

clear all; close all; clc;

path(path, '..');

%% create data structure
data = struct();
relname = sprintf('dataset_%s', datestr(now,'yyyymmdd'));
outfile = sprintf('%s.arff', relname);

% nominal classes
type_class = { 'front', 'middle', 'rear' };

%% populate dataset
for i = 1 : 100
    data(i).idx = i;
    data(i).low = randi([0 33], 1);
    data(i).med = randi([34 66], 1);
    data(i).high = randi([67 100], 1);
    data(i).type_class = type_class{ randi([1 3]) };
end

%% declare nominal specification attributes
nomspec.type_class = type_class;

% save arff
arff_write(outfile, data, relname, nomspec);

%% plot dataset
plot([data.idx], [data.high], 'r.-'); grid on; hold on;
plot([data.idx], [data.med], 'g.-'); grid on; hold on;
plot([data.idx], [data.low], 'b.-'); grid on; hold on;

m_values = mean([ data.high; data.med; data.low ]');

for k = 1 : length(m_values)
    hr = refline(0, m_values(k));
    set(hr,'Color','k','LineStyle','--');
end

legend('high','med','low');

tl = title(relname);
xl = xlabel('idx');
yl = ylabel('value');
set(tl,'Interpreter','none');

set(tl,'FontSize', 14); 
set(xl,'FontSize', 12); 
set(yl,'FontSize', 12);

%% type histogram
T = {data.type_class};
[B,I,J] = unique(T);

f = figure();
hist(J,length(B)); grid on;
xlim([0.5 3.5]);

hp = findobj(f,'Type','patch');
set(hp,'FaceColor','r','EdgeColor','w');

% labels
[n,x] = hist(J,length(B));
text(x, n, type_class, 'horizontalalignment', ...
    'center', 'verticalalignment', 'bottom');

tl = title(relname);
xl = xlabel('class');
yl = ylabel('count');
set(tl,'Interpreter','none');

set(gca,'XTick',[]);
set(tl,'FontSize', 14); 
set(xl,'FontSize', 12); 
set(yl,'FontSize', 12);