Fatal Event Join

Goal: derive each subject's death study day and cause of death by joining their adverse events, and code the cause against a medical dictionary.

Input: one spec.yaml declaring three datasets. DM carries one row per subject. AE carries the adverse-event records: subject, event term, outcome, and study day. MEDDRA carries the dictionary: each lowest-level term beside its preferred term.

Lookups:

• DEATHEV names each subject's fatal adverse event. Only fatal records are eligible, and the latest study day wins; the subject key is shared with the output, so it is inferred rather than restated. A subject with two fatal records takes the later one's day and term, and a subject with no fatal record keeps DTHDY and DTHCAUS blank.
• The named intermediate codes the cause into DTHPTERM: the subject's cause is matched against the dictionary's lowest-level term and the preferred term comes back. A missing cause matches nothing, so the coded cause stays blank too, as it does for a cause the dictionary does not list.

Note: a join never changes the row count: every subject keeps exactly one row, and every read of the same lookup sees the one selected record. When no record is selected, each read answers with a blank rather than failing.