langchain/docs/docs/expression_language/how_to/map.ipynb

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   "source": [
    "---\n",
    "sidebar_position: 0\n",
    "title: \"RunnableParallel: Manipulating data\"\n",
    "keywords: [RunnableParallel, RunnableMap, LCEL]\n",
    "---"
   ]
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    "# Manipulating inputs & output\n",
    "\n",
    "RunnableParallel can be useful for manipulating the output of one Runnable to match the input format of the next Runnable in a sequence.\n",
    "\n",
    "Here the input to prompt is expected to be a map with keys \"context\" and \"question\". The user input is just the question. So we need to get the context using our retriever and passthrough the user input under the \"question\" key.\n",
    "\n",
    "\n"
   ]
  },
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    {
     "data": {
      "text/plain": [
       "'Harrison worked at Kensho.'"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "from langchain.prompts import ChatPromptTemplate\n",
    "from langchain.vectorstores import FAISS\n",
    "from langchain_community.chat_models import ChatOpenAI\n",
    "from langchain_community.embeddings import OpenAIEmbeddings\n",
    "from langchain_core.output_parsers import StrOutputParser\n",
    "from langchain_core.runnables import RunnablePassthrough\n",
    "\n",
    "vectorstore = FAISS.from_texts(\n",
    "    [\"harrison worked at kensho\"], embedding=OpenAIEmbeddings()\n",
    ")\n",
    "retriever = vectorstore.as_retriever()\n",
    "template = \"\"\"Answer the question based only on the following context:\n",
    "{context}\n",
    "\n",
    "Question: {question}\n",
    "\"\"\"\n",
    "prompt = ChatPromptTemplate.from_template(template)\n",
    "model = ChatOpenAI()\n",
    "\n",
    "retrieval_chain = (\n",
    "    {\"context\": retriever, \"question\": RunnablePassthrough()}\n",
    "    | prompt\n",
    "    | model\n",
    "    | StrOutputParser()\n",
    ")\n",
    "\n",
    "retrieval_chain.invoke(\"where did harrison work?\")"
   ]
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    "::: {.callout-tip}\n",
    "Note that when composing a RunnableParallel with another Runnable we don't even need to wrap our dictionary in the RunnableParallel class — the type conversion is handled for us. In the context of a chain, these are equivalent:\n",
    ":::\n",
    "\n",
    "```\n",
    "{\"context\": retriever, \"question\": RunnablePassthrough()}\n",
    "```\n",
    "\n",
    "```\n",
    "RunnableParallel({\"context\": retriever, \"question\": RunnablePassthrough()})\n",
    "```\n",
    "\n",
    "```\n",
    "RunnableParallel(context=retriever, question=RunnablePassthrough())\n",
    "```\n",
    "\n"
   ]
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   "source": [
    "## Using itemgetter as shorthand\n",
    "\n",
    "Note that you can use Python's `itemgetter` as shorthand to extract data from the map when combining with `RunnableParallel`. You can find more information about itemgetter in the [Python Documentation](https://docs.python.org/3/library/operator.html#operator.itemgetter). \n",
    "\n",
    "In the example below, we use itemgetter to extract specific keys from the map:"
   ]
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Harrison ha lavorato a Kensho.'"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "from operator import itemgetter\n",
    "\n",
    "from langchain.prompts import ChatPromptTemplate\n",
    "from langchain.vectorstores import FAISS\n",
    "from langchain_community.chat_models import ChatOpenAI\n",
    "from langchain_community.embeddings import OpenAIEmbeddings\n",
    "from langchain_core.output_parsers import StrOutputParser\n",
    "from langchain_core.runnables import RunnablePassthrough\n",
    "\n",
    "vectorstore = FAISS.from_texts(\n",
    "    [\"harrison worked at kensho\"], embedding=OpenAIEmbeddings()\n",
    ")\n",
    "retriever = vectorstore.as_retriever()\n",
    "\n",
    "template = \"\"\"Answer the question based only on the following context:\n",
    "{context}\n",
    "\n",
    "Question: {question}\n",
    "\n",
    "Answer in the following language: {language}\n",
    "\"\"\"\n",
    "prompt = ChatPromptTemplate.from_template(template)\n",
    "\n",
    "chain = (\n",
    "    {\n",
    "        \"context\": itemgetter(\"question\") | retriever,\n",
    "        \"question\": itemgetter(\"question\"),\n",
    "        \"language\": itemgetter(\"language\"),\n",
    "    }\n",
    "    | prompt\n",
    "    | model\n",
    "    | StrOutputParser()\n",
    ")\n",
    "\n",
    "chain.invoke({\"question\": \"where did harrison work\", \"language\": \"italian\"})"
   ]
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   "source": [
    "## Parallelize steps\n",
    "\n",
    "RunnableParallel (aka. RunnableMap) makes it easy to execute multiple Runnables in parallel, and to return the output of these Runnables as a map."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
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   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'joke': AIMessage(content=\"Why don't bears wear shoes?\\n\\nBecause they have bear feet!\"),\n",
       " 'poem': AIMessage(content=\"In the wild's embrace, bear roams free,\\nStrength and grace, a majestic decree.\")}"
      ]
     },
     "execution_count": 1,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "from langchain.prompts import ChatPromptTemplate\n",
    "from langchain_community.chat_models import ChatOpenAI\n",
    "from langchain_core.runnables import RunnableParallel\n",
    "\n",
    "model = ChatOpenAI()\n",
    "joke_chain = ChatPromptTemplate.from_template(\"tell me a joke about {topic}\") | model\n",
    "poem_chain = (\n",
    "    ChatPromptTemplate.from_template(\"write a 2-line poem about {topic}\") | model\n",
    ")\n",
    "\n",
    "map_chain = RunnableParallel(joke=joke_chain, poem=poem_chain)\n",
    "\n",
    "map_chain.invoke({\"topic\": \"bear\"})"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "833da249-c0d4-4e5b-b3f8-cab549f0f7e1",
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   "source": [
    "## Parallelism\n",
    "\n",
    "RunnableParallel are also useful for running independent processes in parallel, since each Runnable in the map is executed in parallel. For example, we can see our earlier `joke_chain`, `poem_chain` and `map_chain` all have about the same runtime, even though `map_chain` executes both of the other two."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "38e47834-45af-4281-991f-86f150001510",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "958 ms ± 402 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)\n"
     ]
    }
   ],
   "source": [
    "%%timeit\n",
    "\n",
    "joke_chain.invoke({\"topic\": \"bear\"})"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "d0cd40de-b37e-41fa-a2f6-8aaa49f368d6",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1.22 s ± 508 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)\n"
     ]
    }
   ],
   "source": [
    "%%timeit\n",
    "\n",
    "poem_chain.invoke({\"topic\": \"bear\"})"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "799894e1-8e18-4a73-b466-f6aea6af3920",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1.15 s ± 119 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)\n"
     ]
    }
   ],
   "source": [
    "%%timeit\n",
    "\n",
    "map_chain.invoke({\"topic\": \"bear\"})"
   ]
  }
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