Add a clear() method to VectorStoreRetrieverMemory with FAISS vector store

libs/langchain/langchain/memory/vectorstore.py

@@ -73,4 +73,14 @@ def save_context(self, inputs: Dict[str, Any], outputs: Dict[str, str]) -> None:
         self.retriever.add_documents(documents)
 
     def clear(self) -> None:
-        """Nothing to clear."""
+        """Only for faiss vectorstore """
+        """Clear the chat_history in faiss vector_store"""
+        if self.retriever.__dict__['tags'] == ['FAISS']:
+            self.retriever.vectorstore.delete(self.check_history_id())
+        else:
+            raise NotImplementedError("clear method must be implemented by faiss vector store.")
+    def check_history_id(self) -> List[str]:
+        """Check the existed history memory in the faiss retrieval VectorStore."""
+        return list(
+            self.retriever.vectorstore.__dict__["index_to_docstore_id"].values()
+        )