Denote k as the number of features ∈ F∩ A.
if we define: The distance function (metric) should satisfy the following conditions: (1) 0 ≤ Dis (i,C) ≤ 1; (2) if n=m=k then Dis (i,C)=0; (3) if k=0 then Dis (i, C) =1; (4) β > γ > 0, given that insertion is a more difficult operation than deletion; α=0; 1/(m+n) <β < 1/n; and γ = (1-nβ)/m .