ML.NET 使用动态创建预测引擎 Class

Question

我有一个 ML.NET 应用程序，我必须在编译时间后动态创建接口 IDataView 以用于训练。我发现这个 and I've been able to successfully create a dynamic interface for the training data set and then use it to train a model. My problem comes in when I try to use that same interface in order to create a prediction using that trained model. The docs show 你应该创建一个预测引擎，你必须在其中定义输入和输出 class 类型才能创建引擎。类似于：

mlContext.Model.CreatePredictionEngine<TSrc,TDst>(ITransformer, DataViewSchema)

其中 TSrc 和 TDst 是class 编译时已知的类型。我的问题是我在编译时不知道输入 class 类型的结构，必须为输入数据源创建一个动态接口。由于参数已知，因此可以定义输出 class 对象，但我不确定如何进行动态输入。

我想我也许可以尝试在界面上使用类似 GetType() 的东西，但它说“隐式类型的变量不能有多个声明符”。我的简化示例如下所示：

public class ModelOutput
{
    public string PredictedLabel { get; set; }
    public float[] Score { get; set; }
}

public class MakePrediction
{
    protected void Solve(IDataView data, ITransformer model)
    {
        var mlContext = new MLContext();
        var engine = mlContext.Model.CreatePredictionEngine<data.GetType(), ModelOutput>(model, data.Schema);
    }
}

Answer 1

查找MethodInfo.MakeGenericMethod()

Answer 2

可以生成具有 DataViewSchema 中列出的所有字段的运行时 class。这将允许您创建一个 PredictionEngine。

您将无法直接创建 PredictionEngine，您必须调用它。这是一些示例代码：

        // Create runtime type from fields and types in a DataViewSchema
        var runtimeType = ClassFactory.CreateType(dataViewSchema);

        dynamic dynamicPredictionEngine;
        var genericPredictionMethod = mlContext.Model.GetType().GetMethod("CreatePredictionEngine", new[] { typeof(ITransformer), typeof(DataViewSchema) });
        var predictionMethod = genericPredictionMethod.MakeGenericMethod(runtimeType, typeof(PricePrediction));
        dynamicPredictionEngine = predictionMethod.Invoke(mlContext.Model, new object[] { model, dataViewSchema });

要实际使用 PredictionEngine (dynamicPredictionEngine)，请使用与此类似的调用：

var predictMethod = dynamicPredictionEngine.GetType().GetMethod("Predict", new[] { runtimeType });
var predict = predictMethod.Invoke(dynamicPredictionEngine, new[] { inputObject });

我使用了来自 this wonderful example of creating runtime classes 的源代码的修改副本（上面的 ClassFactory）。我的副本接受 DataViewSchema 来自动生成需求 class。该代码如下：

using Microsoft.ML;
using System;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;

public static class ClassFactory
{
    private static AssemblyName _assemblyName;

    public static object CreateObject(string[] PropertyNames, Type[] Types)
    {
        _assemblyName = new AssemblyName("DynamicInput");

        if (PropertyNames.Length != Types.Length)
        {
            Console.WriteLine("The number of property names should match their corresponding types number");
        }

        TypeBuilder DynamicClass = CreateTypeBuilder();
        CreateConstructor(DynamicClass);
        for (int ind = 0; ind < PropertyNames.Count(); ind++)
            CreateProperty(DynamicClass, PropertyNames[ind], Types[ind]);
        Type type = DynamicClass.CreateType();

        return Activator.CreateInstance(type);
    }

    public static Type CreateType(DataViewSchema dataViewSchema)
    {
        _assemblyName = new AssemblyName("DynamicInput");

        TypeBuilder DynamicClass = CreateTypeBuilder();
        CreateConstructor(DynamicClass);
        foreach (var item in dataViewSchema)
        {
            CreateProperty(DynamicClass, item.Name, item.Type.RawType);
        }

        return DynamicClass.CreateType(); 
    }

    private static TypeBuilder CreateTypeBuilder()
    {
        AssemblyBuilder assemblyBuilder = AssemblyBuilder.DefineDynamicAssembly(_assemblyName, AssemblyBuilderAccess.Run);
        ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("MainModule");
        TypeBuilder typeBuilder = moduleBuilder.DefineType(_assemblyName.FullName
                            , TypeAttributes.Public |
                            TypeAttributes.Class |
                            TypeAttributes.AutoClass |
                            TypeAttributes.AnsiClass |
                            TypeAttributes.BeforeFieldInit |
                            TypeAttributes.AutoLayout
                            , null);
        return typeBuilder;
    }

    private static void CreateConstructor(TypeBuilder typeBuilder)
    {
        typeBuilder.DefineDefaultConstructor(MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.RTSpecialName);
    }

    private static void CreateProperty(TypeBuilder typeBuilder, string propertyName, Type propertyType)
    {
        FieldBuilder fieldBuilder = typeBuilder.DefineField("_" + propertyName, propertyType, FieldAttributes.Private);

        PropertyBuilder propertyBuilder = typeBuilder.DefineProperty(propertyName, PropertyAttributes.HasDefault, propertyType, null);
        MethodBuilder getPropMthdBldr = typeBuilder.DefineMethod("get_" + propertyName, MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig, propertyType, Type.EmptyTypes);
        ILGenerator getIl = getPropMthdBldr.GetILGenerator();

        getIl.Emit(OpCodes.Ldarg_0);
        getIl.Emit(OpCodes.Ldfld, fieldBuilder);
        getIl.Emit(OpCodes.Ret);

        MethodBuilder setPropMthdBldr = typeBuilder.DefineMethod("set_" + propertyName,
              MethodAttributes.Public |
              MethodAttributes.SpecialName |
              MethodAttributes.HideBySig,
              null, new[] { propertyType });

        ILGenerator setIl = setPropMthdBldr.GetILGenerator();
        Label modifyProperty = setIl.DefineLabel();
        Label exitSet = setIl.DefineLabel();

        setIl.MarkLabel(modifyProperty);
        setIl.Emit(OpCodes.Ldarg_0);
        setIl.Emit(OpCodes.Ldarg_1);
        setIl.Emit(OpCodes.Stfld, fieldBuilder);

        setIl.Emit(OpCodes.Nop);
        setIl.MarkLabel(exitSet);
        setIl.Emit(OpCodes.Ret);

        propertyBuilder.SetGetMethod(getPropMthdBldr);
        propertyBuilder.SetSetMethod(setPropMthdBldr);
    }
}

ML.NET 使用动态创建预测引擎 Class

ML.NET Create Prediction Engine using Dynamic Class

c#

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