c# - 使用 Accord.Net 框架的决策树

Question

我正在尝试学习如何在 C# 中实现决策树。我发现的例子对我没有帮助。我想做的是为用户报告的问题提供解决方案，我有一个包含三千个问题和答案的数据库。我正在使用 dotnet 并尝试使用 Accord.net 框架，但是我没有得到它，我需要有关如何实现的示例或提示。

正如我所说，我有一个包含旧问题和答案的数据库，将用于训练算法并为 future 问题提供可能的答案。

附注我正在使用 Visual Studio Community 2017。

Answer 1

有助于理解如何将这个问题映射到决策树问题的第一件事是:每个问题都应该被视为决策树中的一个 split 节点(或一个决策节点)，以及给出的答案的集合每个问题都有助于形成每个 split 节点的子节点。在您的这种情况下，我们将把每个问题视为数据表的一列，并将表的每一行视为为每个问题提供的一组答案。要注意的第二件事是决策树需要预测“某事”，在您的情况下，它是其中一个问题的答案，我们将其视为表中的最后一列。由于没有提供书面示例，我假设了一个医学数据库，其中包含一组问题和一组答案，如下面的代码所示。您可以轻松地将其映射到任何其他数据类型，只要它也是一组问题和答案。预测列/问题是下面给出的示例中诊断的疾病。

[ - 这段代码的灵感来自@http://accord-framework.net/docs/html/T_Accord_MachineLearning_DecisionTrees_Learning_ID3Learning.htm]提供的示例

[- 先决条件:您需要安装 Accord.Net 软件包:Install-Package Accord.MachineLearning]

using Accord.MachineLearning.DecisionTrees;
using Accord.MachineLearning.DecisionTrees.Learning;
using Accord.Math.Optimization.Losses;
using System;
using System.Data;
using Accord.Statistics.Filters;
using System.Linq;
using Accord.Math;

namespace DecisionTreeExamples
{
    public class QandADecisionTree{

    public static void QandADecisionTreeExample()
    {
        // Step1: Since there was no sample provided in this question, we first construct our data
        DataTable data = new DataTable("QandA");

        // Step2: Adding questions. Each question is a column in the data table. 
        PopulateQuestions(data); /*Note that the last column/question is the prediction column. */

        // Step3: Adding the history of 6 patients and the corresponding diagnosis (This is also our training data)
        PopulateAnswers(data);

        //Step4: Next we need to convert our data table to its numerical representation, which is what ID3 algorithm expects as input.
        Codification codification = new Codification(data);
        DataTable codifiedData = codification.Apply(data);

        //Note: specify all the columns except the last column, which is the value that the decision tree should predict, 
        int[][] input = codifiedData.ToJagged<int>("Are you above 50 years old?",
                                                   "What is your gender?",
                                                   "Do you have headache?",
                                                   "Has your blood pressure gone above 12 in the last 30 days?",
                                                   "Do you have a running nose?",
                                                   "Do you have a soat throat?",
                                                   "Do you have fever?");

        int[] predictions = codifiedData.ToArray<int>("Diagnosed Disease");

        // Step4: produce Decision tree.
        ID3Learning decisionTreeLearningAlgorithm = new ID3Learning { };

        DecisionTree decisionTree = decisionTreeLearningAlgorithm.Learn(input, predictions);

        // Step5: Use the produced decision tree on a test data
        int[] query = codification.Transform(new[,]{ {"Are you above 50 years old?","no" },
                                                   { "What is your gender?","male" },
                                                   { "Do you have headache?" ,"yes"},
                                                   { "Has your blood pressure gone above 12 in the last 30 days?","no" },
                                                   { "Do you have a running nose?","yes" },
                                                   { "Do you have a soat throat?" ,"yes"},
                                                   { "Do you have fever?" ,"yes"} });

        int result = decisionTree.Decide(query);
        string diagnosis = codification.Revert("Diagnosed Disease", result);

        Console.WriteLine($"Diagnosed disease: {diagnosis}"); // Prints Common Cold
    }

    /// <summary>
    /// Populates data table with questions, that in this example each question happens to be a column. 
    /// </summary>
    /// <param name="data">Specifies the data base in this example which is a collection of questions and answers.</param>
    private static void PopulateQuestions(DataTable data)
    {
        data.Columns.Add(new DataColumn("Are you above 50 years old?", typeof(string))); //Q1
        data.Columns.Add(new DataColumn("What is your gender?", typeof(string))); //Q2
        data.Columns.Add(new DataColumn("Do you have headache?", typeof(string))); //Q3
        data.Columns.Add(new DataColumn("Has your blood pressure gone above 12 in the last 30 days?", typeof(string))); //Q4
        data.Columns.Add(new DataColumn("Do you have a running nose?", typeof(string))); //Q5
        data.Columns.Add(new DataColumn("Do you have a soat throat?", typeof(string))); //Q6
        data.Columns.Add(new DataColumn("Do you have fever?", typeof(string))); //Q7
        data.Columns.Add(new DataColumn("Diagnosed Disease", typeof(string))); // Prediction Column
    }

    /// <summary>
    /// Populates data table with rows, that in this example each row happens to represent a patient, and each column, except the last one is a question. The value of a column in a row means the reponse patient provided to that question.
    /// </summary>
    /// <param name="data">Specifies the data base in this example which is a collection of questions and answers.</param>
    private static void PopulateAnswers(DataTable data)
    {
        var patient1 = data.NewRow();
        patient1["Are you above 50 years old?"] = "no";
        patient1["What is your gender?"] = "male";
        patient1["Do you have headache?"] = "yes";
        patient1["Has your blood pressure gone above 12 in the last 30 days?"] = "no";
        patient1["Do you have a running nose?"] = "yes";
        patient1["Do you have a soat throat?"] = "yes";
        patient1["Do you have fever?"] = "yes";
        patient1["Diagnosed Disease"] = "Common Cold";
        data.Rows.Add(patient1);

        var patient2 = data.NewRow();
        patient2["Are you above 50 years old?"] = "yes";
        patient2["What is your gender?"] = "female";
        patient2["Do you have headache?"] = "yes";
        patient2["Has your blood pressure gone above 12 in the last 30 days?"] = "yes";
        patient2["Do you have a running nose?"] = "no";
        patient2["Do you have a soat throat?"] = "no";
        patient2["Do you have fever?"] = "no";
        patient2["Diagnosed Disease"] = "High Blood Pressure";
        data.Rows.Add(patient2);


        var patient3 = data.NewRow();
        patient3["Are you above 50 years old?"] = "yes";
        patient3["What is your gender?"] = "male";
        patient3["Do you have headache?"] = "yes";
        patient3["Has your blood pressure gone above 12 in the last 30 days?"] = "yes";
        patient3["Do you have a running nose?"] = "no";
        patient3["Do you have a soat throat?"] = "no";
        patient3["Do you have fever?"] = "no";
        patient3["Diagnosed Disease"] = "High Blood Pressure";
        data.Rows.Add(patient3);

        var patient4 = data.NewRow();
        patient4["Are you above 50 years old?"] = "no";
        patient4["What is your gender?"] = "female";
        patient4["Do you have headache?"] = "yes";
        patient4["Has your blood pressure gone above 12 in the last 30 days?"] = "no";
        patient4["Do you have a running nose?"] = "yes";
        patient4["Do you have a soat throat?"] = "yes";
        patient4["Do you have fever?"] = "yes";
        patient4["Diagnosed Disease"] = "Common Cold";
        data.Rows.Add(patient4);

        var patient5 = data.NewRow();
        patient5["Are you above 50 years old?"] = "yes";
        patient5["What is your gender?"] = "female";
        patient5["Do you have headache?"] = "yes";
        patient5["Has your blood pressure gone above 12 in the last 30 days?"] = "no";
        patient5["Do you have a running nose?"] = "yes";
        patient5["Do you have a soat throat?"] = "yes";
        patient5["Do you have fever?"] = "yes";
        patient5["Diagnosed Disease"] = "Common Cold";
        data.Rows.Add(patient5);

        var patient6 = data.NewRow();
        patient6["Are you above 50 years old?"] = "yes";
        patient6["What is your gender?"] = "female";
        patient6["Do you have headache?"] = "no";
        patient6["Has your blood pressure gone above 12 in the last 30 days?"] = "yes";
        patient6["Do you have a running nose?"] = "no";
        patient6["Do you have a soat throat?"] = "no";
        patient6["Do you have fever?"] = "no";
        patient6["Diagnosed Disease"] = "High Blood Pressure";
        data.Rows.Add(patient6);
    }

}
}