Refactor create_hierarchy_dict function to concisely include additional hierarchy levels

isco.py

@@ -20,19 +20,11 @@ def create_hierarchy_dict(file: str) -> dict:
     with open(file, newline="") as csvfile:
         reader = csv.DictReader(csvfile)
         for row in reader:
-            # Extract unit group level code (4 digits)
             unit_code = row["unit"].zfill(4)
-
-            # Extract the parent code for the unit group level, which is the minor group level (3 digits)
             minor_code = unit_code[0:3]
-
-            # Add the unit code to the hierarchy with its parent code
-            isco_hierarchy[unit_code] = {minor_code}
-
-            # Additionally, we can add the parent's parent codes at the sub-major group level (2 digits) and major group level (1 digit)
             sub_major_code = unit_code[0:2]
             major_code = unit_code[0]
-            isco_hierarchy[unit_code].update({major_code, sub_major_code})
+            isco_hierarchy[unit_code] = {minor_code, major_code, sub_major_code}
 
     return isco_hierarchy