R: Lower and Upper Triangular Part of a Matrix

lower.tri {base} | R Documentation

## Lower and Upper Triangular Part of a Matrix

### Description

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

### Usage

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

### Arguments

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

### See Also

`diag`, `matrix`.

### Examples

    m2 <- ma <- matrix(1:20, 4, 5)
    m2[lower.tri(m2)] <- NA
    m2
    stopifnot(lower.tri(ma) == !upper.tri(ma, diag=TRUE))

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