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\name{upperTriangle}
\alias{upperTriangle}
\alias{upperTriangle<-}
\alias{lowerTriangle}
\alias{lowerTriangle<-}
\title{Extract or replace the upper/lower triangular portion of a matrix}
\description{
Extract or replace the upper/lower triangular portion of a matrix.
}
\usage{
upperTriangle(x, diag=FALSE, byrow=FALSE)
upperTriangle(x, diag=FALSE, byrow=FALSE) <- value
lowerTriangle(x, diag=FALSE, byrow=FALSE)
lowerTriangle(x, diag=FALSE, byrow=FALSE) <- value
}
\arguments{
\item{x}{Matrix}
\item{diag}{Logical. If \code{TRUE}, include the matrix diagonal.}
\item{byrow}{Logical. If \code{FALSE}, return/replace elements in
column-wise order. If \code{TRUE}, return/replace elements in
row-wise order.}
\item{value}{Either a single value or a vector of length equal to that
of the current upper/lower triangular. Should be of a mode which
can be coerced to that of \code{x}.}
}
\value{
\code{upperTriangle(x)} and \code{lowerTriangle(x)} return the upper
or lower triangle of matrix x, respectively. The assignment forms
replace the upper or lower triangular area of the
matrix with the provided value(s).
}
\note{
By default, the elements are returned/replaced in R's default column-wise
order. Thus
\preformatted{lowerTriangle(x) <- upperTriangle(x)}
will not yield a symmetric matrix. Instead use:
\preformatted{lowerTriangle(x) <- upperTriangle(x, byrow=TRUE)}
or equivalently:
\preformatted{lowerTriangle(x, byrow=TRUE) <- upperTriangle(x)}
}
\author{Gregory R. Warnes \email{greg@warnes.net}}
\seealso{
\code{\link[base]{diag}},
\code{\link[base]{lower.tri}},
\code{\link[base]{upper.tri}}
}
\examples{
x <- matrix(1:25, nrow=5, ncol=5)
x
upperTriangle(x)
upperTriangle(x, diag=TRUE)
upperTriangle(x, diag=TRUE, byrow=TRUE)
lowerTriangle(x)
lowerTriangle(x, diag=TRUE)
lowerTriangle(x, diag=TRUE, byrow=TRUE)
upperTriangle(x) <- NA
x
upperTriangle(x, diag=TRUE) <- 1:15
x
lowerTriangle(x) <- NA
x
lowerTriangle(x, diag=TRUE) <- 1:15
x
## Copy lower triangle into upper triangle to make
## the matrix (diagonally) symmetric
x <- matrix(LETTERS[1:25], nrow=5, ncol=5, byrow=TRUE)
x
lowerTriangle(x) = upperTriangle(x, byrow=TRUE)
x
}
\keyword{array}
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