R: Lower and Upper Triangular Part of a Matrix

lower.tri {base}

R Documentation

Lower and Upper Triangular Part of a Matrix

Returns a matrix of logicals the same size of a given matrix with entries TRUE in the lower or upper triangle.

lower.tri(x, diag = FALSE)
upper.tri(x, diag = FALSE)

`x`	a matrix.
`diag`	logical. Should the diagonal be included?

(m2 <- matrix(1:20, 4, 5))
lower.tri(m2)
m2[lower.tri(m2)] <- NA
m2