dummytable.m

function Tdummy = dummytable(T)
% Tdummy = dummytable(T) - convert categorical variables in table to dummy
% variables
%
% This functions takes the categorical variables in a table and converts
% them to separate dummy variables with intelligent names.  This way they
% can be used in the Classification Learner App and the variable names make
% sense for feature selection, etc.
%
% Usage:
%
%     Tdummy = dummytable(T)
%
% Inputs:
%
%     T:        Table with categoricals or categorical variable
%
% Outputs: 
%
%     Tdummy:   T with categorical variables turned into dummy variables with
%               intelligent names
%
% Example:
%
%        % Simple Table
%        T = table(rand(10,1),categorical(cellstr('rbbgbgbbgr'.')),...
%           'VariableNames',{'Percent','Color'});
%        disp(T)
% 
%        % Turn it into a dummy table 
%        Tdummy = dummytable(T);
%        disp(Tdummy)
%
% See Also: dummyvar, table, categorical, classificationLearner

% Copyright 2017 The MathWorks, Inc.
% Sean de Wolski Apr 13, 2014

    % Error checking
    narginchk(1,1)    
    validateattributes(T,{'categorical', 'table'},{},mfilename,'T',1);
    
    % If it's a categorical, do out best to convert it to a table with an
    % intelligent variable name
    if iscategorical(T)
        % Try to use existing variable name
        cname = inputname(1);
        if isempty(cname)
            % It's a MATLAB Expression, default to Var1
            cname = 'Var1';
        end
        T = table(T,'VariableNames',{cname});
    end 
       
    % Identify categoricals and their names
    cats = varfun(@iscategorical,T,'OutputFormat','uniform');
    
    % Short circuit if there are no categoricals
    if ~any(cats)
        Tdummy = T;
        return
    end            
            
    % Store everything in a cell.  w will be the total width of the table
    % with each variable dummyvar'd
    w = nnz(~cats)+sum(varfun(@(x)numel(categories(x)),T(:,cats),'OutputFormat','uniform'));
    
    % Preallocate storage
    datastorage = cell(1,w);
    namestorage = cell(1,w);
    
    % Engine
    idx = 0; % Start nowhere in cell
    for ii = 1:width(T)
        idx = idx+1;
        % Loop over table deciding what to do with each variable
        if cats(ii)
            % It's a categorical,
            % Extract it and build keep its categories and dummyvar
            Tii = T{:,ii};
            categoriesii = categories(Tii)';
            ncatii = numel(categoriesii); % How many?

            % Build dummy var as a row cell with columns in each
            dvii = num2cell(dummyvar(Tii), 1); % Dummy var then cell                                    
            
            % Build names
            namesii = strcat(T.Properties.VariableNames{ii}, '_', categoriesii);
            
            % Insert
            datastorage(idx:(idx+ncatii-1)) = dvii;
            namestorage(idx:(idx+ncatii-1)) = namesii;
            
            % Increment
            idx = idx+ncatii-1;                        
            
        else
            % Extract non categorical into current storage location
            datastorage{idx} = T{:,ii};
            namestorage(idx) = T.Properties.VariableNames(ii);
        end
    end
    
    % Build Tdummy with comma separated list expansion
    Tdummy = table(datastorage{:},'VariableNames',matlab.lang.makeValidName(namestorage));

end