Row and column indices around the diagonal of a square matrix

For each diagonal position i of a length x length matrix, returns the indices of the diagonal cell and of its two neighbours in the same row: the cell to the right (just above the diagonal, column i + 1) and the cell to the left (just below the diagonal, column i - 1).

Usage

off_diagonal_index(length)

Arguments

length

Integer (at least 1). Number of rows and columns of the square matrix.

Value

A data frame (not a matrix) with length rows and four numeric columns:

x1

Row index i.

x2

Column index of the diagonal cell (same as x1).

x3

Column index of the cell to the right, i + 1; in the last row this is length + 1, outside the matrix.

x4

Column index of the cell to the left, i - 1; in the first row this is 0, outside the matrix.

See also

matrix_triangle

Examples

off_diagonal_index(length=6)
#>   x1 x2 x3 x4
#> 1  1  1  2  0
#> 2  2  2  3  1
#> 3  3  3  4  2
#> 4  4  4  5  3
#> 5  5  5  6  4
#> 6  6  6  7  5