
Object-Oriented Programming in R 97
consisted of a set of R environments; see Section 2.2.4.3 for more details on
this data type. These environments were used as hash tables and access to the
data was through functions such as mget and the operators $ and [[. However,
as the metadata have grown and b ecome more complex, this approach is
no longer tenable and a switch to a lightweight database implementation is
underway. For more details on database interfaces, see Chapter 8.4.
The implementation of the database interface has relied on the use of func-
tions to directly access the underlying data tables. But such use is not con-
sistent with using the ...