我如何从dist给出的单元格返回行和列号

Question

说我有

> x<-1:5
> dist(x)
  1 2 3 4
2 1      
3 2 1    
4 3 2 1  
5 4 3 2 1
> which(dist(x)==max(dist(x)))
[1] 4

如何从索引4返回到行号和列号(5,1)？

Answer 1

可能有一个更整洁的方式......

dist.x <- dist(x)
which(as.matrix(dist.x) == max(dist.x) & lower.tri(dist.x), arr.ind=TRUE)
#   row col
# 5   5   1

Answer 2

dist有一个as.matrix方法，它很有用。你可以试试这个：

kk <- as.matrix(dist(x))
which(kk == max(kk), arr.ind=TRUE)

对于您的示例，

  row col
5   5   1
1   1   5

Answer 3

dist返回类“dist”的对象。您应该首先阅读帮助文件，其中包含：

Value

dist returns an object of class "dist".

The lower triangle of the distance matrix stored by columns in a vector, say do. If n is the number of observations, i.e., n <- attr(do, "Size"), then for i < j ≤ n, the dissimilarity between (row) i and j is do[n*(i-1) - i*(i-1)/2 + j-i]. The length of the vector is n*(n-1)/2, i.e., of order n^2.

发布的其他答案会以有用的方式修改“dist”对象。