测试运行结果：
>ma <- matrix(c(1:4, 1, 6:8), nrow = 2)
>ma
[,1] [,2] [,3] [,4]
[1,]1317
[2,]2468
>apply(ma, 2, function(x)x/(mean(x)))
[,1] [,2] [,3] [,4]
[1,] 0.6666667 0.8571429 0.2857143 0.9333333
[2,] 1.3333333 1.1428571 1.7142857 1.0666667
apply函数参数帮助。
apply(X, MARGIN, FUN, ...)
Arguments
X
an array, including a matrix.
MARGIN
a vector giving the subscripts which the function will be applied over. E.g., for a matrix 1 indicates rows, 2 indicates columns, c(1, 2) indicates rows and columns. Where X has named dimnames, it can be a character vector selecting dimension names.
FUN
the function to be applied: see ‘Details’. In the case of functions like +, %*%, etc., the function name must be backquoted or quoted.
...
optional arguments to FUN.
不慢。数据标准化，将数据按比例缩放，使之落入一个小的特定区间。去除数据的单位限制，将其转化为无量纲的纯数值，便于不同单位或量级的指标能够进行比较和加权。
所有R的函数和数据集是保存在程序包里面的。只有当一个包被载入时，它的内容才可以被访问。
