router runnable (#8496)

Co-authored-by: Nuno Campos <nuno@boringbits.io>

docs/extras/guides/expression_language/cookbook.ipynb

@@ -22,10 +22,19 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 4,
+   "execution_count": 1,
    "id": "466b65b3",
    "metadata": {},
-   "outputs": [],
+   "outputs": [
+    {
+     "name": "stderr",
+     "output_type": "stream",
+     "text": [
+      "/Users/harrisonchase/.pyenv/versions/3.9.1/envs/langchain/lib/python3.9/site-packages/deeplake/util/check_latest_version.py:32: UserWarning: A newer version of deeplake (3.6.14) is available. It's recommended that you update to the latest version using `pip install -U deeplake`.\n",
+      "  warnings.warn(\n"
+     ]
+    }
+   ],
    "source": [
     "from langchain.prompts import ChatPromptTemplate\n",
     "from langchain.chat_models import ChatOpenAI"
@@ -33,7 +42,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": 2,
    "id": "3c634ef0",
    "metadata": {},
    "outputs": [],
@@ -583,6 +592,98 @@
     "chain2.invoke({})"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "d094d637",
+   "metadata": {},
+   "source": [
+    "## Router\n",
+    "\n",
+    "You can also use the router runnable to conditionally route inputs to different runnables."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "id": "252625fd",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from langchain.chains import create_tagging_chain_pydantic\n",
+    "from pydantic import BaseModel, Field\n",
+    "\n",
+    "class PromptToUse(BaseModel):\n",
+    "    \"\"\"Used to determine which prompt to use to answer the user's input.\"\"\"\n",
+    "    \n",
+    "    name: str = Field(description=\"Should be one of `math` or `english`\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "id": "57886e84",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "tagger = create_tagging_chain_pydantic(PromptToUse, ChatOpenAI(temperature=0))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "id": "a303b089",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "chain1 = ChatPromptTemplate.from_template(\"You are a math genius. Answer the question: {question}\") | ChatOpenAI()\n",
+    "chain2 = ChatPromptTemplate.from_template(\"You are an english major. Answer the question: {question}\") | ChatOpenAI()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "id": "7aa9ea06",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from langchain.schema.runnable import RouterRunnable\n",
+    "router = RouterRunnable({\"math\": chain1, \"english\": chain2})"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "id": "6a3d3f5d",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "chain = {\n",
+    "    \"key\": {\"input\": lambda x: x[\"question\"]} | tagger | (lambda x: x['text'].name),\n",
+    "    \"input\": {\"question\": lambda x: x[\"question\"]}\n",
+    "} | router"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "id": "8aeda930",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "AIMessage(content='Thank you for the compliment! The sum of 2 + 2 is equal to 4.', additional_kwargs={}, example=False)"
+      ]
+     },
+     "execution_count": 9,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "chain.invoke({\"question\": \"whats 2 + 2\"})"
+   ]
+  },
   {
    "cell_type": "markdown",
    "id": "29781123",