Langchain JS MapReduce - how to override default combine_prompt with custom prompt template

[poetsmeniet]

Hi all!

I've implemented a simple Mapreduce in javascript, Node, and it seems to be working fine. I used the documentation here:
https://js.langchain.com/docs/modules/chains/document/map_reduce

I've done a lot of searching, but am unable to override the combine_prompt that is defined in dist/chains/question_answering/map_reduce_prompts.js.

I know how to create a custom prompt template.

So given the following code, where do I pass my custom prompt template?

const model = new OpenAI({ temperature: 0, maxConcurrency: 10 }); const chain = loadQAMapReduceChain(model); const docs = [ new Document({ pageContent: "harrison went to harvard" }), new Document({ pageContent: "ankush went to princeton" }), ]; const res = await chain.call({ input_documents: docs, question: "Where did harrison go to college", }); console.log({ res });

[dosubot[bot]]

🤖

Hello @poetsmeniet! Good to see you again. Hope you're doing well with your project.

To override the default combine_prompt with a custom prompt template in LangChain JS MapReduce, you can pass your custom prompt template as a parameter when calling the loadQAMapReduceChain function.

Here's an example of how you can do this:

import { PromptTemplate } from "langchain/prompts";

// Define your custom prompt
const customPrompt = PromptTemplate.fromTemplate(`Your custom template {variable}`);

// Load the QA MapReduce chain with your custom prompt
const chain = loadQAMapReduceChain(model, { combinePrompt: customPrompt });

// Your existing code...
const docs = [
  new Document({ pageContent: "harrison went to harvard" }),
  new Document({ pageContent: "ankush went to princeton" }),
];
const res = await chain.call({
  input_documents: docs,
  question: "Where did harrison go to college",
});
console.log({ res });

In this example, customPrompt is your custom prompt template. You create an instance of PromptTemplate from your custom template string and pass it as the combinePrompt parameter when calling loadQAMapReduceChain.

This is based on the structure of the loadQAMapReduceChain function, which accepts an object of type MapReduceQAChainParams as its second parameter. This object can have a combinePrompt property, which is used as the prompt template for the combine phase of the MapReduce process. If combinePrompt is not provided, the function uses a default prompt template.

For more information, you can refer to the source code of the loadQAMapReduceChain function.

I hope this helps! Let me know if you have any other questions.

Sources

• loadQAMapReduceChain : combineMapPrompt & combinePrompt failing with "Missing value for input ..."
• Custom prompt in summarization chain
• examples/src/prompts/pipeline_prompt.ts
• langchain/src/chains/question_answering/load.ts

---

This response is meant to be useful and save you time. It is not meant to be a precise solution, but rather a starting point for your own research.

Help me be more useful! Please leave a 👍 if this is helpful and 👎 if it is irrelevant.

If you want to continue the conversation, start your reply with @dosu-bot.