c# - 如何在应用预测器之前从 ML.Net 管道返回转换后的数据

Question

这是从 TaxiFarePrediction 示例复制的 ML.Net 管道对象的创建。

        LearningPipeline pipeline = new LearningPipeline
        {
            new TextLoader(TrainDataPath).CreateFrom<TaxiTrip>(separator:','),
            new ColumnCopier(("FareAmount", "Label")),
            new CategoricalOneHotVectorizer("VendorId","RateCode","PaymentType"),
            new ColumnConcatenator("Features","VendorId","RateCode","PassengerCount","TripDistance","PaymentType"),
            new FastTreeRegressor()
        };

本质上，我想在应用 ColumnCopier、CategoricalOneHotVectorizer 和 ColumnConcatenator 之后返回数据。

Answer 1

用于调试器中的可视化 Microsoft 编程类

LearningPipelineDebugProxy

该类有两个信息量很大的字段：行和列。当然，用于调试的类并不是很容易创建，因为它是内部密封的：

namespace Microsoft.ML
{
  /// <summary>
  /// The debug proxy class for a LearningPipeline.
  /// Displays the current columns and values in the debugger Watch window.
  /// </summary>
  internal sealed class LearningPipelineDebugProxy
  {

根据源代码。在这种情况下，如果调试器可视化还不够，我会使用反射。为了在 TaxiTrip 实例中创建 LearningPipelineDebugProxy 实例，我使用了以下技巧：

1. 通过 CreateInstance 方法创建 LearningPipelineDebugProxy 的实例
2. 添加了通过反射获取所需字段的方法。

在代码中，该片段看起来像这样：

    public static PredictionModel<TaxiTrip, TaxiTripFarePrediction> Train()
    {
        var pipeline = new LearningPipeline();
        pipeline.Add(new TextLoader(_datapath).CreateFrom<TaxiTrip>(useHeader: true, separator: ','));


        Type obj = AppDomain.CurrentDomain.GetAssemblies().SelectMany(t => t.GetTypes()).
            Where(t => String.Equals(t.Name, "LearningPipelineDebugProxy", StringComparison.Ordinal)).First();


        var instObject = Activator.CreateInstance(obj, new []{pipeline});

        pipeline.Add(new ColumnCopier(("FareAmount", "Label")));
        pipeline.Add(new CategoricalOneHotVectorizer("VendorId", "RateCode", "PaymentType"));
        pipeline.Add(new ColumnConcatenator("Features", "VendorId", "RateCode", "PassengerCount", "TripDistance", "PaymentType"));

        var rws = GetPropValue(instObject, "Rows");
        var clms = GetPropValue(instObject, "Columns");

        pipeline.Add(new FastTreeRegressor());

        PredictionModel<TaxiTrip, TaxiTripFarePrediction> model = pipeline.Train<TaxiTrip, TaxiTripFarePrediction>();
        return model;
    }

    public static object GetPropValue(object src, string propName)
    {
        return src.GetType().GetProperty(propName).GetValue(src, null);
    }

在调试器窗口中，不仅在调试器中，行变得可用：