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这里是关于LangChain框架中的提示词模板使用的技巧，希望可以帮助到大家，欢迎大家的补充和纠正

一、使用LangChain的提示词模板：技巧与总结

1、格式化示例集

我们可以使用使用FewShotPromptTemplate来格式化示例集

const examples = [{question: "Who lived longer, Muhammad Ali or Alan Turing?",answer: `Are follow up questions needed here: Yes.Follow up: How old was Muhammad Ali when he died?Intermediate answer: Muhammad Ali was 74 years old when he died.Follow up: How old was Alan Turing when he died?Intermediate answer: Alan Turing was 41 years old when he died.So the final answer is: Muhammad Ali`,},{question: "When was the founder of craigslist born?",answer: `Are follow up questions needed here: Yes.Follow up: Who was the founder of craigslist?Intermediate answer: Craigslist was founded by Craig Newmark.Follow up: When was Craig Newmark born?Intermediate answer: Craig Newmark was born on December 6, 1952.So the final answer is: December 6, 1952`,},{question: "Who was the maternal grandfather of George Washington?",answer: `Are follow up questions needed here: Yes.Follow up: Who was the mother of George Washington?Intermediate answer: The mother of George Washington was Mary Ball Washington.Follow up: Who was the father of Mary Ball Washington?Intermediate answer: The father of Mary Ball Washington was Joseph Ball.So the final answer is: Joseph Ball`,},{question:"Are both the directors of Jaws and Casino Royale from the same country?",answer: `Are follow up questions needed here: Yes.Follow up: Who is the director of Jaws?Intermediate Answer: The director of Jaws is Steven Spielberg.Follow up: Where is Steven Spielberg from?Intermediate Answer: The United States.Follow up: Who is the director of Casino Royale?Intermediate Answer: The director of Casino Royale is Martin Campbell.Follow up: Where is Martin Campbell from?Intermediate Answer: New Zealand.So the final answer is: No`,},
];const examplePrompt = PromptTemplate.fromTemplate("Question:{question} \n {answer}"
)const prompt = new FewShotPromptTemplate({examples,examplePrompt,suffix: "Question:{input}",inputVariables: ["input"]
})const formatted = await prompt.format({input: "Who was the father of Mary Ball Washington?"
})console.log(formatted)

最后输出的示例中，会将examples中的示例加入到提示词模板的前面，组合成为完整的示例

//提示词模板输出结果
Question:Who lived longer, Muhammad Ali or Alan Turing? Are follow up questions needed here: Yes.Follow up: How old was Muhammad Ali when he died?Intermediate answer: Muhammad Ali was 74 years old when he died.Follow up: How old was Alan Turing when he died?Intermediate answer: Alan Turing was 41 years old when he died.So the final answer is: Muhammad AliQuestion:When was the founder of craigslist born? Are follow up questions needed here: Yes.Follow up: Who was the founder of craigslist?Intermediate answer: Craigslist was founded by Craig Newmark.Follow up: When was Craig Newmark born?Intermediate answer: Craig Newmark was born on December 6, 1952.So the final answer is: December 6, 1952Question:Who was the maternal grandfather of George Washington? Are follow up questions needed here: Yes.Follow up: Who was the mother of George Washington?Intermediate answer: The mother of George Washington was Mary Ball Washington.Follow up: Who was the father of Mary Ball Washington?Intermediate answer: The father of Mary Ball Washington was Joseph Ball.So the final answer is: Joseph BallQuestion:Are both the directors of Jaws and Casino Royale from the same country? Are follow up questions needed here: Yes.Follow up: Who is the director of Jaws?Intermediate Answer: The director of Jaws is Steven Spielberg.Follow up: Where is Steven Spielberg from?Intermediate Answer: The United States.Follow up: Who is the director of Casino Royale?Intermediate Answer: The director of Casino Royale is Martin Campbell.Follow up: Where is Martin Campbell from?Intermediate Answer: New Zealand.So the final answer is: NoQuestion:Who was the father of Mary Ball Washington?

2、示例选择器来组合提示词模板

我们可以使用 SemanticSimilarityExampleSelector类来使用嵌入模型来计算输入样本和少数样本之间的相似性，并使用向量存储来执行最近邻搜索

let AzureOpenAIEmbedding = await getAzureEmbeddings()const exampleSelecttor = await SemanticSimilarityExampleSelector.fromExamples(examples,AzureOpenAIEmbedding,MemoryVectorStore,{k: 1}
)
const question = "Who was the father of Mary Ball Washington?"
const selectedExamples = await exampleSelecttor.selectExamples({ question })
console.log("🚀 ~ mainScript2 ~ selectedExamples:", selectedExamples)、/**
🚀 ~ mainScript2 ~ selectedExamples: [{question: 'Who was the maternal grandfather of George Washington?',answer: '\n' +'  Are follow up questions needed here: Yes.\n' +'  Follow up: Who was the mother of George Washington?\n' +'  Intermediate answer: The mother of George Washington was Mary Ball Washington.\n' +'  Follow up: Who was the father of Mary Ball Washington?\n' +'  Intermediate answer: The father of Mary Ball Washington was Joseph Ball.\n' +'  So the final answer is: Joseph Ball\n' +'  '}
]
**/

当调用exampleSelecttor中的selectExamples方法的时候，它会根据输入的question来使用向量搜索从示例集中找出与输入的问题最相似的示例集

3、在聊天模型中使用合适的少数示例

在提示词结构中有一个重要的概念是示例，给大模型的输入中提供示例会让输出结果更加精准，而示例选择器可以实现一个效果：根据用户的输入选择合适的示例

在langchian中是可以实现这个功能的，使用SemanticSimilarityExampleSelector示例选择器，根据用户的输入使用向量数据库匹配更加合适的例子

实现步骤：

• 先准备一些示例数据-最好是数组形式的
• 然后再实例化向量大模型
• 创建好向量数据库
• 使用模型选择器

完整的代码如下：

  //1、先准备一个例子，这个例子是数组对象类型的，对象需要拥有input哥outputconst examples = [{ input: "2+2", output: "4" },{ input: "2+3", output: "5" },{ input: "2+4", output: "6" },{ input: "What did the cow say to the moon?", output: "nothing at all" },{input: "Write me a poem about the moon",output:"One for the moon, and one for me, who are we to talk about the moon?",},];//2、从例子中格式化数据，准备好插入到向量数据库中const toVectorize=examples.map((examples)=>`${examples.input}${examples.output}`)//3、实例化向量数据库的查询const vectorStore=await MemoryVectorStore.fromTexts(toVectorize,examples,await getAzureEmbeddings())//4、创建一个选择器const exampleSelect=new SemanticSimilarityExampleSelector({vectorStore,k:1})//5、使用const result=await exampleSelect.selectExamples({input:"hourse"})// console.log("🚀 ~ mainScript4 ~ result:", result)//6、和动态模版添加方法组合const messsageTemplate=ChatPromptTemplate.fromMessages([["user","{input}"],["ai","{output}"]])const fewPrompt=new FewShotChatMessagePromptTemplate({examplePrompt:messsageTemplate,// examples:result,exampleSelector:exampleSelect,inputVariables:['input']})//  //原文档有bug，这里是修复的，不可以直接传入fewShotPrompt，而是需要实例化一下，封装成为消息类型const finalPrompt=ChatPromptTemplate.fromMessages([["system","You are a wondrous wizard of math."],ChatPromptTemplate.fromMessages((await fewPrompt.invoke({})).toChatMessages()),["user","{input}"],])//7、模型结合使用const azureModel=await getAzureModel()const chain = finalPrompt.pipe(azureModel);console.log(await chain.invoke({ input: "What's 3+3?" }))

4、如何部分格式化提示词模板

想要对提示模板进行部分分配的一个常见用例是，如果您在其他变量之前访问提示中的某些变量。例如，假设您有一个需要两个变量（foo 和 baz）的提示模板。如果你在链的早期获得 foo 值，但后来获得 baz 值，那么在链中完全传递这两个变量可能会很不方便。相反，你可以用 foo 值对 prompt 模板进行部分化处理，然后传递部分 prompt 模板并使用它

// 第一种使用，在partial方法中进行实例化
const prompt = new PromptTemplate({template: "{foo}{bar}",inputVariables: ["foo", "bar"]
})const partialPrompt = await prompt.partial({foo: "foo"
})const fromattedPrompt = await partialPrompt.format({bar: "baz"
})console.log(fromattedPrompt)// 第二种使用，在模板初始化中进行实例化
const prompt = new PromptTemplate({template: "{foo}{bar}",inputVariables: ["bar"],partialVariables: {foo: "foo"}
})const formattedPrompt = await prompt.format({bar: "baz",
})
// console.log("🚀 ~ mainScript2 ~ formattedPrompt:", formattedPrompt)