as.matrix: Convert a data.table to a matrix

Description

Converts a data.table into a matrix, optionally using one of the columns in the data.table as the matrix rownames.

Usage

# S3 method for data.table
as.matrix(x, rownames=NULL, rownames.value=NULL, ...)

Value

A new matrix containing the contents of x.

Arguments

x: a data.table
rownames: optional, a single column name or column number to use as the rownames in the returned matrix. If TRUE the key of the data.table will be used if it is a single column, otherwise the first column in the data.table will be used.
rownames.value: optional, a vector of values to be used as the rownames in the returned matrix. It must be the same length as nrow(x).
...: Required to be present because the generic `as.matrix` generic has it. Arguments here are not currently used or passed on by this method.

Details

as.matrix is a generic function in base R. It dispatches to as.matrix.data.table if its x argument is a data.table.

The method for data.tables will return a character matrix if there are 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 an integer matrix, etc.

Examples

Run this code

DT <- data.table(A = letters[1:10], X = 1:10, Y = 11:20)
as.matrix(DT) # character matrix
as.matrix(DT, rownames = "A")
as.matrix(DT, rownames = 1)
as.matrix(DT, rownames = TRUE)

setkey(DT, A)
as.matrix(DT, rownames = TRUE)

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