用R计算矩阵中对称数据的平均值

Question

假设我有一个这样的矩阵：

A = matrix( 
  c(2, 4, 3, 1, 5, 7, 4, 5, 1), # the data elements 
  nrow=3,              # number of rows 
  ncol=3,              # number of columns 
  byrow = TRUE
)     

> A
     [,1] [,2] [,3]
[1,]    2    4    3
[2,]    1    5    7
[3,]    4    5    1

现在我想计算这个矩阵中对称数据的平均值，就像这样：

> A.mean
     [,1] [,2] [,3]
[1,]  2.0  2.5  3.5
[2,]  2.5  5.0  6.0
[3,]  3.5  6.0  1.0

如何在不使用循环的情况下执行此操作？

Answer 1

试试吧：

(A+t(A))/2
#     [,1] [,2] [,3]
#[1,]  2.0  2.5  3.5
#[2,]  2.5  5.0  6.0
#[3,]  3.5  6.0  1.0

Answer 2

另一个选项是Reduce

Reduce(`+`, list(A, t(A)))/2
#     [,1] [,2] [,3]
#[1,]  2.0  2.5  3.5
#[2,]  2.5  5.0  6.0
#[3,]  3.5  6.0  1.0