source: prextra/randomforestc.m @ 86

%
%          W = RANDOMFORESTC(A,L,N)
%
% Train a decision forest on A, using L decision trees, each trained on
% a bootstrapped version of dataset A. Each decison tree is using random
% feature subsets of size N in each node.  When N=0, no feature subsets
% are used.

% C-code:  train:  101.3 s    110.4
%          test:     0.1 s      0.1
% matlab:  train: 1726.9 s
%          test:   520.4 s
function w = randomforestc(a,L,featsubset)

if nargin<3
        featsubset = 1;
end
if nargin<2
        L = 50;
end
if nargin<1 || isempty(a)
        w = mapping(mfilename,{L,featsubset});
        w = setname(w,'Random forest (L=%d)',L);
        return
end

if ~ismapping(L)
        isvaldfile(a,2,2); % at least 2 obj/class, 2 classes
        opt = [];
        [n,dim,opt.K] = getsize(a);
        opt.featsubset = featsubset;
        v = cell(L,1);
        for i=1:L
                [x,z] = gendat(a);
        if exist('decisiontree')==3
            v{i} = decisiontree(+x,getnlab(x),opt.K,opt.featsubset);
        else
                v{i} = tree_train(+x,getnlab(x),opt);
        end
        end
        w = mapping(mfilename,'trained',v,getlablist(a),dim,opt.K);
        w = setname(w,'Random forest (L=%d)',L);
else
        v = getdata(L);
        n = size(a,1);  % nr objects
        K = size(L,2);  % nr of classes
        nrv = length(v); % nr of trees
    out = zeros(n,K);
    if exist('decisiontree')==3
        for j=1:nrv
            I = decisiontree(v{j},+a);
            out = out + accumarray([(1:n)' I],ones(n,1));
        end
    else
        % the old fashioned slow Matlab code
        for i=1:n
            x = +a(i,:);
            for j=1:nrv
                I = tree_eval(v{j},x);
                out(i,I) = out(i,I)+1;
            end
        end
        out = out./repmat(sum(out,2),1,K);
    end
        w = setdat(a,out,L);
end
return