R语言做数据中心化和标准化scale函数手动实现
1. R中的方差和标准差方差：var，是样本方差var(y) instructs R to calculate the sample variance of Y. In other words it uses n-1 ‘degrees of freedom’, where n is the number of observations in Y.标准差：sd，是样本标准差var(y) instructs R to calculate the sample variance of Y. In o
