title: 'Could not determine an IDataView type for member features' when call MakePredictionFunction
body: <p>I'm trying to make prediction function using new Microsoft.ML 0.6.0</p>
  
  <p>When i call "model.AsDynamic.MakePredictionFunction", I receive </p>
  
  <blockquote>
    <p>"System.ArgumentOutOfRangeException: 'Could not determine an IDataView
    type for member features'".</p>
  </blockquote>
  
  <p>Code:</p>
  
  <pre><code>using System;
  using Microsoft.ML;
  using Microsoft.ML.Runtime.Api;
  using Microsoft.ML.Runtime.Data;
  using Microsoft.ML.Trainers;
  using Microsoft.ML.StaticPipe;
  
  namespace MachineLearning
  {
      class MLTest
      {
          public void Run()
          {
              var env = new LocalEnvironment();
              var reader = TextLoader.CreateReader(env, ctx =&gt; (label: ctx.LoadBool(0), features: ctx.LoadFloat(1, 3)));
              var traindata = reader.Read(new MultiFileSource("train.txt"));
              var bctx = new BinaryClassificationContext(env);
              var est = reader.MakeNewEstimator()
                  .Append(x =&gt; (x.label, prediction: bctx.Trainers.Sdca(x.label, x.features.Normalize())));
              var model = est.Fit(traindata);
  
              //FAILS: System.ArgumentOutOfRangeException: 'Could not determine an IDataView type for member features'
              var predictionFunct = model.AsDynamic.MakePredictionFunction&lt;Issue, Prediction&gt;(env);
  
          }
  
          public class Issue
          {
              public float label;
              public Vector&lt;float&gt; features; //what is wrong?
          }
  
          public class Prediction
          {
              [ColumnName("prediction.predictedLabel")]
              public bool PredictionLabel;
  
              [ColumnName("prediction.probability")]
              public float Probability;
  
              [ColumnName("prediction.score")]
              public float Score;
          }
      }
  }
  </code></pre>
  
  <p>File train.txt contains:</p>
  
  <pre><code>1   0   0   0
  1   0   1   0
  1   0   0   1
  1   0   1   1
  0   1   1   1
  0   1   0   1
  0   1   1   0
  0   1   0   0
  </code></pre>
  
  <p>It looks like error is in class "Issue", but what exactly is wrong? Thanks</p>