fix duplicate vobj for same slug

lektor_groupby/util.py

@@ -1,5 +1,8 @@
 from lektor.reporter import reporter, style
 
+from typing import List
+from itertools import groupby
+
 
 def report_config_error(key: str, field: str, val: str, e: Exception) -> None:
     ''' Send error message to Lektor reporter. Indicate which field is bad. '''
@@ -9,3 +12,16 @@ def report_config_error(key: str, field: str, val: str, e: Exception) -> None:
         reporter._write_line(style(msg, fg='red'))
     except Exception:
         print(msg)  # fallback in case Lektor API changes
+
+
+def most_used_key(keys: List[str]) -> str:
+    if len(keys) < 3:
+        return keys[0]  # TODO: first vs last occurrence
+    best_count = 0
+    best_key = ''
+    for key, itr in groupby(keys):
+        count = sum(1 for i in itr)
+        if count > best_count:  # TODO: (>) vs (>=), first vs last occurrence
+            best_count = count
+            best_key = key
+    return best_key