| lower.tri {base} | R Documentation | 
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