1.基尼指数: Gini(p)=∑k=1Kpk(1−pk)\operatorname{Gini}(p)=\sum_{k=1}^{K} p_{k}\left(1-p_{k}\right)Gini(p)=∑k=1Kpk(1−pk) 特征A的条件下,集合D的基尼指数: GGG in i (D,A)=∣D1∣∣D∣Gini(D1)+∣D2∣∣D∣G(D, A)=\frac{\left|D_{1}\right|}{|D|} \operatorname{Gin} i\left(D_{1}\right)+\frac{\left|D_{2}\right|}{|D|} G(D,A)=∣D∣∣D1∣Gini(D1)+∣D∣∣D2∣G in i(D2)i\left(D_{2}\right)i(D2)