data.matrix {base} | R Documentation |

## 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. |

### Details

Supplying a data frame with columns which are not numeric, factor or logical
is an error. A warning is given if any non-factor column has a class,
as then information can be lost.

### 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`

.

Otherwise, the result of `as.matrix`

.

### Note

The default behaviour for data frames differs from **R** < 2.5.0 which
always gave the result character rownames.

### 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.

### See Also

`as.matrix`

,
`data.frame`

,
`matrix`

.

### Examples

DF <- data.frame(a=1:3, b=letters[10:12],
c=seq(as.Date("2004-01-01"), by = "week", len = 3),
stringsAsFactors = TRUE)
data.matrix(DF[1:2])
data.matrix(DF) # gives a warning and quotes dates as #days since 1970.

[Package

*base* version 2.5.0

Index]