Fix multiple subset matching

simplebooks.py

@@ -115,7 +115,7 @@ class SimpleBooks(datasets.GeneratorBasedBuilder):
     def _generate_examples(self, subset, split, files):
         _id = 0
         for path, file in files:
-            if subset in path and split in path:
+            if path.startswith(f"{subset}/") and split in path:
                 for line in file:
                     yield _id, {"text": line.strip()}
                     _id += 1