title: Unhandled Exception: System.ArgumentOutOfRangeException: Schema mismatch for feature column 'Features': expected Vector<R4>, got Vector<R8>
body: <p>I am trying to write a basic 'hello world' type program to predict the values of the XOR function. This is the error message I am getting:</p>
  
  <pre><code>Unhandled Exception: System.ArgumentOutOfRangeException: Schema mismatch for feature column 'Features': expected Vector&lt;R4&gt;, got Vector&lt;R8&gt;
  </code></pre>
  
  <p>Parameter name: inputSchema
  This is my code:</p>
  
  <pre><code>type Sample = {
      X: float
      Y: float
      Result: float
  }
  
  let createSample x y result = {X = x; Y = y; Result = result}
  
  let solveXOR() =
      let problem = 
          [
              createSample 0.0 0.0 0.0
              createSample 1.0 0.0 1.0
              createSample 0.0 1.0 1.0
              createSample 1.0 0.0 0.0
          ]
  
      let context = new MLContext()
      let data = context.Data.ReadFromEnumerable(problem)
  
      let pipeline = 
          context.Transforms
              .Concatenate("Features", "X", "Y")
              .Append(context.Transforms.CopyColumns(inputColumnName = "Result", outputColumnName = "Label"))
              //.Append(context.Transforms.Conversion.MapKeyToVector("X"))
              //.Append(context.Transforms.Conversion.MapKeyToVector("Y"))
              .AppendCacheCheckpoint(context)
              .Append(context.Regression.Trainers.FastTree())
  
      let model = pipeline.Fit(data)
  
      let predictions = model.Transform(data)
      let metrics = context.BinaryClassification.Evaluate(predictions)
  
      printfn "Accuracy %f" metrics.Accuracy
  </code></pre>
  
  <p>Any pointers as to what I am doing wrong would be greatly appreciated.</p>