r - 为矩阵中的 "offset"对角线赋值

Question

如果我有一个矩阵 x任意维度，对于这个例子:

     [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    0    0    0
[2,]    0    0    0    0    0
[3,]    0    0    0    0    0
[4,]    0    0    0    0    0
[5,]    0    0    0    0    0

我想从某一列开始将 0 更改为 1，然后向下移动一个，向右移动一个，直到最后一列结束。因此，如果我从 [,3] 列开始改变会导致

     [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    1    0    0
[2,]    0    0    0    1    0
[3,]    0    0    0    0    1
[4,]    0    0    0    0    0
[5,]    0    0    0    0    0

我想也许是这样的x[,3:ncol(x)][1:ncol(x)] <- 1但这给了我

     [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    1    0    0
[2,]    0    0    1    0    0
[3,]    0    0    1    0    0
[4,]    0    0    1    0    0
[5,]    0    0    1    0    0

Answer 1

你也可以使用row和col:

start_col <- 3
m[row(m) + start_col - 1 == col(m)] <- 1

m    
#      [,1] [,2] [,3] [,4] [,5]
# [1,]    0    0    1    0    0
# [2,]    0    0    0    1    0
# [3,]    0    0    0    0    1
# [4,]    0    0    0    0    0
# [5,]    0    0    0    0    0

m 是:

m <- matrix(0, ncol = 5, nrow = 5)