diag {base} | R Documentation |
Extract or replace the diagonal of a matrix, or construct a diagonal matrix.
diag(x = 1, nrow, ncol= ) diag(x) <- value
x |
a matrix, vector or 1D array. |
nrow, ncol |
Optional dimensions for the result. |
value |
either a single value or a vector of length equal to that
of the current diagonal. Should be of a mode which can be coerced
to that of x . |
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).
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.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
require(stats) 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