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.

% Authors:
%   Valerio De Carolis          <valerio.decarolis@gmail.com>
%
%  28 September 2012 - University of Rome "La Sapienza" 

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')
        
        % use unique temp dir
        %   support multiple calls of arff_read in parallel with the same input file
        outdir = tempname;
        
        % 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)
        % Erase '[]().'
        if ~isempty(find(fields{fn}=='[' | fields{fn}==']' | fields{fn}=='(' | fields{fn}==')' | fields{fn}=='.'))
            s = fields{fn};
            fields{fn} = s(s~='[' & s~=']' & s~='(' & s~=')' & s~='.');
        end

        % Replace '-' with '_'
        if ismember('-',fields{fn})
            s = fields{fn};
            s(strfind(s,'-')) = '_';
            fields{fn} = s;
        end
        
        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 directory and decompressed file
    if exist('dec_files','var') && ~isempty(dec_files)
        delete(dec_files{1});
        rmdir(outdir, 's');
    end

end

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