r - 如何让对角线和反向对角线穿过 2D 矩阵中的一个点？

Question

我有以下矩阵（本身），我想找到它的对角线和给定其中任意点的反向对角线。我能想到算法，但我不确定什么 R 函数可以帮助我实现它。就像我知道如何访问所有穿过该点的行和列一样，所以我想也许还有一个技巧可以找到对角线。我想最终将每个对角线保存在一个向量中。

x = matrix(data=c(
  "E","E","o","4","E","E","E",
  "E","E","m","5","E","E","E",
  "E","E","n","5","E","E","E",
  "E","E","e","5","E","E","E",
  "E","E","e","4","E","E","E",
  "E","E","r","E","E","E","E"
), nrow=6, ncol=7, byrow=TRUE)

r=3
c=5

row=x[3,]
col=x[,5]
reverse_diagonal=x[i,j] in which (i+j==3+5)
diagonal=x[i,j] in which (i-j==3-5)

Answer 1

对角线：

x[row(x) - col(x) == r - c]
# [1] "o" "5" "E" "E" "E"

反向对角线：

x[row(x) + col(x) == r + c]
# [1] "E" "e" "5" "E" "E" "E"

我建议您运行以下命令以了解其工作原理：

row(x)
col(x)
row(x) - col(x)
row(x) - col(x) == r - c
x[row(x) - col(x) == r - c]