If one of `nrow`

or `ncol`

is not given, an attempt is
made to infer it from the length of `data`

and the other
parameter. If neither is given, a one-column matrix is returned.

If there are too few elements in `data`

to fill the matrix,
then the elements in `data`

are recycled. If `data`

has
length zero, `NA`

of an appropriate type is used for atomic
vectors (`0`

for raw vectors) and `NULL`

for lists.

`is.matrix`

returns `TRUE`

if `x`

is a vector and has a
`"dim"`

attribute of length 2) and `FALSE`

otherwise.
Note that a `data.frame`

is **not** a matrix by this
test. The function is generic: you can write methods to handle
specific classes of objects, see InternalMethods.

`as.matrix`

is a generic function. The method for data frames
will return a character matrix if there is only atomic columns and any
non-(numeric/logical/complex) column, applying `as.vector`

to factors and `format`

to other non-character columns.
Otherwise, the usual coercion hierarchy (logical < integer < double <
complex) will be used, e.g., all-logical data frames will be coerced
to a logical matrix, mixed logical-integer will give a integer matrix,
etc.

The default method for `as.matrix`

calls `as.vector(x)`

, and
hence e.g.coerces factors to character vectors.

When coercing a vector, it produces a one-column matrix, and
promotes the names (if any) of the vector to the rownames of the matrix.

`is.matrix`

is a primitive function.

The `print`

method for a matrix gives a rectangular layout with
dimnames or indices. For a list matrix, the entries of length not
one are printed in the form `integer,7` indicating the type
and length.