There are multiple transformations involved in using the Drug Strength table. Firstly, the conceptual representation of drug strength is spread across amount, numerator, and/or a denominator. Additionally, for each of the 3, there is a value and a unit, where the unit is represented as a concept id.
The Drug Strength table is prepared in advance as the Drug Strength Staged table, where the value and unit are mapped and represented in their final form. For the staged value, the form takes on that of a varchar (string) with a mathematical expression of the fraction that can be evaluated later on.
To stage the Drug Strength table, it is first processed. All the invalid entries in the Drug Strength table are filtered out and the related fields, invalid_reason, valid_start_date, and valid_end_date are removed. Since it has little relevance to the use cases seen in this package, box_size is also removed.
The unit concept ids are also mapped to their concept names.
The result of this function call is a Drug Strength Processed table. This is the table that is used to stage the value and unit fields and it is prerequisite for the next staging step.
ds_stage()