This function converts data (such as a factor) to numeric values
in order that the user may calculate, for example,
the mean, variance, covariance and correlation of the data.
If x
is a numeric vector or integer vector, it is returned
unchanged.
If x
is a logical vector, it is converted to a 0-1 matrix with
2 columns. The first column contains a 1 if the logical value is
FALSE
, and the second column contains a 1 if the logical
value is TRUE
.
If x
is a complex vector, it is converted to a matrix with 2
columns, containing the real and imaginary parts.
If x
is a factor, the result is a matrix of 0-1 dummy
variables. The matrix has one column for each possible level of the
factor. The (i,j)
entry is
equal to 1 when the i
th factor value equals the
j
th level, and is equal to 0 otherwise.
If x
is a matrix or data frame, the appropriate conversion is
applied to each column of x
.
Note that, unlike model.matrix
, this command converts a
factor into a full set of dummy variables (one column for each level of
the factor).