source: prextra/tree_train.m @ 99

Last change on this file since 99 was 27, checked in by dtax, 13 years ago

This is obviously also needed... Here they are!

File size: 1.1 KB
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1%
2%    w = tree_train(x,y,opt)
3%
4function w = tree_train(x,y,opt)
5
6% how good are we in this node?
7err = tree_gini(y,opt.K);
8if (err==0)
9
10        w = y(1); % just predict this label
11
12else
13        % we split further
14        n = size(x,1);
15
16        % optionally, choose only from a subset
17        if (opt.featsubset>0)
18                fss = randperm(size(x,2));
19                fss = fss(1:opt.featsubset);
20        else
21                fss = 1:size(x,2);
22        end
23
24        % check each feature separately:
25        besterr = inf; bestf = []; bestt = []; bestj = []; bestI = [];
26        for i=fss
27                % sort the data along feature i:
28                [xi,I] = sort(x(:,i)); yi = y(I);
29                % run over all possible splits:
30                for j=1:n-1
31                        % compute the gini
32                        err = j*tree_gini(yi(1:j),opt.K) + (n-j)*tree_gini(yi(j+1:n),opt.K);
33                        % and see if it is better than before.
34                        if (err<besterr)
35                                besterr = err;
36                                bestf = i;
37                                bestj = j;
38                                bestt = mean(xi(j:j+1));
39                                bestI = I;
40                        end
41                end
42        end
43
44        % store
45        w.bestf = bestf;
46        w.bestt = bestt;
47        %  now find the children:
48        w.l = tree_train(x(bestI(1:bestj),:),y(bestI(1:bestj)),opt);
49        w.r = tree_train(x(bestI(bestj+1:end),:),y(bestI(bestj+1:end)),opt);
50end
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