data.matrix: Convert a Data Frame to a Numeric Matrix

Description

Return the matrix obtained by converting all the variables in a data
frame to numeric mode and then binding them together as the columns of
a matrix. Factors and ordered factors are replaced by their internal
codes.

Usage

data.matrix(frame, rownames.force = NA)

Arguments

frame

a data frame whose components are logical vectors,
factors or numeric vectors.

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.

Value

If frame inherits from class "data.frame", an integer or
numeric matrix of the same dimensions as frame, with dimnames
taken from the row.names (or NULL, depending on
rownames.force) and names.

Logical and factor columns are converted to integers. Any other
column which is not numeric (according to is.numeric) is
converted by as.numeric or, for S4 objects,
as(, "numeric"). If all columns are integer (after
conversion) the result is an integer matrix, otherwise a numeric
(double) matrix.

References

Chambers, J. M. (1992)
Data for models.
Chapter 3 of Statistical Models in S
eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole.