matrix

From base v3.0.3 by R-core R-core@R-project.org

Matrices

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.

Keywords: algebra, array

Usage

matrix(data = NA, nrow = 1, ncol = 1, byrow = FALSE, dimnames = NULL)
as.matrix(x, ...)
"as.matrix"(x, rownames.force = NA, ...)
is.matrix(x)

Arguments

data: an optional data vector (including a list or expression vector). Non-atomic classed R objects are coerced by as.vector and all attributes discarded.
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 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.

Note

If you just want to convert a vector to a matrix, something like

  dim(x) <- c(nx, ny)
  dimnames(x) <- list(row_names, col_names)

will avoid duplicating x.

References

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

Examples

library(base)

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

Documentation reproduced from package base, version 3.0.3, License: Part of R 3.0.3

Community examples

baraboshkin-evgenij@ya.ru at May 28, 2019 base v3.6.0

``` ma <- matrix( month.abb[c(12, 1:11)], nrow = 3, dimnames = list( c("start", "middle", "end"), c("Winter", "Spring", "Summer", "Fall") ) ) ma[, "Winter"] # to access the data by column name ```

mark@niemannross.com at Nov 5, 2018 base v3.5.1

Example files for [LinkedIn Learning: R for Data Science, lunchbreak Learning](https://linkedin-learning.pxf.io/rweekly_matrix) ```r # matrix is a vector or list with 2 dimensions # (Matrix is a 2-dimension Array. Array is like stacked matrices) I.am.a.vector <- c("twas","brillig","and","the","slithey","toves") I.am.a.matrix <- matrix(I.am.a.vector,nrow=2,ncol=3) I.am.a.matrix I.am.a.matrix[2,3] dim(I.am.a.matrix) # byrow I.am.a.matrix <- matrix(I.am.a.vector,nrow=2,ncol=3,byrow=TRUE) I.am.a.matrix I.am.a.matrix <- matrix(I.am.a.vector,nrow=2,ncol=3,byrow=FALSE) I.am.a.matrix # dimnames lots.o.letters <- c(letters[1:10],LETTERS[1:10]) letter.matrix <- matrix(lots.o.letters,ncol = 2,dimnames = list(c(),c("lowercase","UPPERCASE"))) letter.matrix # or by row letter.matrix <- matrix(lots.o.letters,nrow = 2,dimnames = list(c("lowercase","UPPERCASE"),c())) letter.matrix #transpose matrix.transposed <- t(I.am.a.matrix) matrix.transposed[2,3] #oops matrix.transposed[3,2] #works because there are now 3 rows and 2 columns ```

richie@datacamp.com at Jan 19, 2017 base v3.3.2

![matrix-glyphs](http://i.giphy.com/m5kfULGaiUmHu.gif) ## Basic usage Create a matrix by passing an atomic vector, and the number of rows and columns. ```{r} matrix(month.abb, nrow = 3, ncol = 4) ``` Actually, you don't need to specify both the number of rows *and* the number of columns. You can specify one, and `matrix()` will automatically guess the other using the length of the vector. ```{r} matrix(month.abb, nrow = 3) matrix(month.abb, ncol = 4) ``` ## `byrow` argument The elements are added the matrix one column at a time. You can change it so they are added one column at a time using `byrow = TRUE`. For comparison, see the transpose function, [`t()`](https://www.rdocumentation.org/packages/base/topics/t). ```{r} matrix(month.abb, nrow = 4, byrow = TRUE) t(matrix(month.abb, nrow = 3)) ``` ## `dimnames` argument In the same way that a vector can have named elements, a matrix can have row and column names. `dimnames` must be specified as a `list` containing two `character` vectors. The first character vector contains the row names, and the second contains the column names. ```{r} matrix( month.abb[c(12, 1:11)], nrow = 3, dimnames = list( c("start", "middle", "end"), c("Winter", "Spring", "Summer", "Fall") ) ) ``` You can also give names to the dimensions by making `dimnames` a named list. ```{r} matrix( month.abb[c(12, 1:11)], nrow = 3, dimnames = list( position = c("start", "middle", "end"), season = c("Winter", "Spring", "Summer", "Fall") ) ) ``` ## List matrices As well as atomic vectors, you can create a matrix from a `list`. In this case, each element of the matrix is a list. ```{r} prime_seqs <- list( 2, 3, 4:5, 6:7, 8:11, 12:13, 14:17, 18:19, 20:23 ) (prime_matrix <- matrix(prime_seqs, nrow = 3)) prime_matrix[3, 2] ```