function?res?=?calculateImpurity（examples_）
????P1?=?0;
????P2?=?0;
????[m_n_]?=?size（examples_）;
????P1?=?sum（examples_（:n_）?==?‘是‘）;
????P2?=?sum（examples_（:n_）?==?‘否‘）;
????P1?=?P1?/?m_;
????P2?=?P2?/?m_;
????if?P1?==?1?||?P1?==?0
????????res?=?0;
????else
????????res?=?-（P1*log2（P1）+P2*log2（P2））;
????end
end

?屬性????????????大小?????日期????時間???名稱
-----------?---------??----------?-----??----

?????文件????????331??2019-10-27?23:49??calculateImpurity.m

?????文件????????938??2019-10-27?12:45??data.txt

?????文件???????2718??2019-10-22?18:22??Decision?Tree.md

?????文件????????376??2019-10-28?14:02??decisionTree.m

?????文件????????384??2019-10-28?01:49??drawTree.asv

?????文件???????1441??2019-10-28?13:58??drawTree.m

?????文件???????1745??2019-10-27?23:19??getBestlabel.asv

?????文件???????1833??2019-10-28?00:18??getBestlabel.m

?????文件???????1475??2019-10-28?12:24??makeTree.asv

?????文件???????1485??2019-10-28?12:27??makeTree.m

?????文件????????770??2019-10-27?23:54??watermalon.mat

-----------?---------??----------?-----??----

????????????????13496????????????????????11