平均对角减去一

Question

是否可以计算矩阵对角线下对角线的平均值？

    a1  a2  a3  a4  a5
a1  0   1   1   1   1
a2  2   0   1   1   1
a3  1   3   0   1   1
a4  1   1   4   0   1
a5  1   1   1   5   0

我想计算2 + 3 + 4 + 5的平均值

Answer 1

是.我认为(和R一样)有各种各样的方法,但这里有一个.它使用diagbase-R中的函数,并在获取对角线并计算它的平均值之前删除第一行和最后一列.

res <- mean(diag(mm[-1,-ncol(mm)]))

使用的数据:

mm <- structure(c(0L, 2L, 1L, 1L, 1L, 1L, 0L, 3L, 1L, 1L, 1L, 1L, 0L, 
4L, 1L, 1L, 1L, 1L, 0L, 5L, 1L, 1L, 1L, 1L, 0L), .Dim = c(5L, 
5L), .Dimnames = list(c("a1", "a2", "a3", "a4", "a5"), c("a1", 
"a2", "a3", "a4", "a5")))

Answer 2

这是一种可能性

mean(m[col(m) == (row(m) - 1)])
## [1] 3.5

这里的想法是获取列和行索引,然后只选择列==行-1时的值(正好在对角线下方-对角线是col ==行)

数据

m <- structure(c(0L, 2L, 1L, 1L, 1L, 1L, 0L, 3L, 1L, 1L, 1L, 1L, 0L, 
4L, 1L, 1L, 1L, 1L, 0L, 5L, 1L, 1L, 1L, 1L, 0L), .Dim = c(5L, 
5L), .Dimnames = list(c("a1", "a2", "a3", "a4", "a5"), c("a1", 
"a2", "a3", "a4", "a5")))