diag {base}

R Documentation

Matrix Diagonals

Description

Extract or replace the diagonal of a matrix, or construct a diagonal matrix.

Usage

diag(x = 1, nrow, ncol)
diag(x) <- value

Arguments

x	a matrix, vector or 1D array.
nrow, ncol	Optional dimensions for the result.

Value

If x is a matrix then diag(x) returns the diagonal of x. The resulting vector will have names if the matrix x has matching column and row names.

If x is a vector (or 1D array) of length two or more, then diag(x) returns a diagonal matrix whose diagonal is x.

If x is a vector of length one then diag(x) returns an identity matrix of order the nearest integer to x. The dimension of the returned matrix can be specified by nrow and ncol (the default is square).

The assignment form sets the diagonal of the matrix x to the given value(s).

Note

Using diag(x) can have unexpected effects if x is a vector that could be of length one. Use diag(x, nrow = length(x)) for consistent behaviour.

See Also

matrix.

Examples

dim(diag(3))
diag(10,3,4) # guess what?
all(diag(1:3) == {m <- matrix(0,3,3); diag(m) <- 1:3; m})

diag(var(M <- cbind(X=1:5, Y=rnorm(5))))#-> vector with names "X" and "Y"
rownames(M) <- c(colnames(M),rep("",3));
M; diag(M) #  named as well

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