Feature faiss delete (#8135)

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- Description: docstore had two main method: add and search, however,
dealing with docstore sometimes requires deleting an entry from
docstore. So I have added a simple delete method that deletes items from
docstore. Additionally, I have added the delete method to faiss
vectorstore for the very same reason.
  - Issue: NA
  - Dependencies: NA
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---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

docs/extras/integrations/vectorstores/faiss.ipynb

@@ -80,7 +80,7 @@
    "source": [
     "from langchain.document_loaders import TextLoader\n",
     "\n",
-    "loader = TextLoader(\"../../../state_of_the_union.txt\")\n",
+    "loader = TextLoader(\"../../../extras/modules/state_of_the_union.txt\")\n",
     "documents = loader.load()\n",
     "text_splitter = CharacterTextSplitter(chunk_size=1000, chunk_overlap=0)\n",
     "docs = text_splitter.split_documents(documents)\n",
@@ -90,7 +90,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 11,
+   "execution_count": 3,
    "id": "5eabdb75",
    "metadata": {
     "tags": []
@@ -517,6 +517,67 @@
     "for doc in results:\n",
     "    print(f\"Content: {doc.page_content}, Metadata: {doc.metadata}\")"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "1becca53",
+   "metadata": {},
+   "source": [
+    "## Delete\n",
+    "\n",
+    "You can also delete ids. Note that the ids to delete should be the ids in the docstore."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "id": "1408b870",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "True"
+      ]
+     },
+     "execution_count": 4,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "db.delete([db.index_to_docstore_id[0]])"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "id": "d13daf33",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "False"
+      ]
+     },
+     "execution_count": 6,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# Is now missing\n",
+    "0 in db.index_to_docstore_id"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "30ace43e",
+   "metadata": {},
+   "outputs": [],
+   "source": []
   }
  ],
  "metadata": {