8.2.5.6 categorical.double

Method: out = double (obj)

Convert to double array, by getting the underlying code values.

Converts obj to a string array. The doubles will be the underlying numeric code values of obj, or NaN for undefined values.

The numeric code values of two different categorical arrays do *not* necessarily correspond to the same string values, and can *not* be meaningfully compared for equality or ordering.

Returns a double array the same size as obj.