Convert a Data Frame into a Numeric Matrix
DESCRIPTION:
This function takes a data frame as an argument and returns a matrix of numeric data whose elements correspond to the elements of the data frame.
USAGE: 
data.matrix(frame)
REQUIRED ARGUMENTS:
frame:
a data frame, or else a frame that inherits from class "data.frame" (design or model frame).
VALUE:
a numeric matrix containing the numeric information in frame. The matrix has a column for each numeric vector, a set of columns for each matrix, and a column for each factor in frame. Factors are first transformed to numeric values using codes(). If factors are present in frame, the matrix returned has an attribute called "column.levels", a list with an element for each column of the matrix. The elements of this list are either NULL or else contain the levels of the factors prior to conversion by codes().
SEE ALSO:
as.matrix , codes , model.matrix .
EXAMPLES: 
cu.summary[1:5,]


# returns the following:
                Price Country Reliability Mileage  Type
Acura Integra 4 11950   Japan Much better      NA Small
   Dodge Colt 4  6851   Japan          NA      NA Small
   Dodge Omni 4  6995     USA  Much worse      NA Small
 Eagle Summit 4  8895     USA      better      33 Small
Ford Escort   4  7402     USA       worse      33 Small


data.matrix(cu.summary[1:5,])


# returns the following:
                Price Country Reliability Mileage Type
Acura Integra 4 11950       5           5      NA    4
   Dodge Colt 4  6851       5          NA      NA    4
   Dodge Omni 4  6995      10           1      NA    4
 Eagle Summit 4  8895      10           4      33    4
Ford Escort   4  7402      10           2      33    4