R: Matrices

matrix {base}

R Documentation

Matrices

Description

matrix creates a matrix from the given set of values.

as.matrix attempts to turn its argument into a matrix.

is.matrix tests if its argument is a (strict) matrix.

Usage

matrix(data = NA, nrow = 1, ncol = 1, byrow = FALSE,
       dimnames = NULL)

as.matrix(x, ...)
## S3 method for class 'data.frame'
as.matrix(x, rownames.force = NA, ...)

is.matrix(x)

Arguments

data

an optional data vector.

nrow

the desired number of rows.

ncol

the desired number of columns.

byrow

logical. If FALSE (the default) the matrix is filled by columns, otherwise the matrix is filled by rows.

dimnames

A dimnames attribute for the matrix: NULL or a list of length 2 giving the row and column names respectively. An empty list is treated as NULL, and a list of length one as row names. The list can be named, and the list names will be used as names for the dimensions.

x

an R object.

...

additional arguments to be passed to or from methods.

rownames.force

logical indicating if the resulting matrix should have character (rather than NULL) rownames. The default, NA, uses NULL rownames if the data frame has ‘automatic’ row.names or for a zero-row data frame.

Details

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 array, 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 matrix and has a dim attribute of length 2) and FALSE otherwise. Note that a data.frame is not a matrix by this test. It 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 any non-(numeric/logical/complex) column, applying format to 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.

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.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

Examples

is.matrix(as.matrix(1:10))
!is.matrix(warpbreaks)# data.frame, NOT matrix!
warpbreaks[1:10,]
as.matrix(warpbreaks[1:10,]) #using as.matrix.data.frame(.) method

# Example of setting row and column names
mdat <- matrix(c(1,2,3, 11,12,13), nrow = 2, ncol=3, byrow=TRUE,
               dimnames = list(c("row1", "row2"),
                               c("C.1", "C.2", "C.3")))
mdat

[Package base version 2.9.0 ]