This code is part of the ML.NET taxi fare prediction demo.

mlnet-taxidemo-rmse.cs

// get a set of predictions 
Console.Write("Evaluating the model....");
var predictions = model.Transform(partitions.TestSet);

// get regression metrics to score the model
var metrics = mlContext.Regression.Evaluate(predictions, "Label", "Score");
Console.WriteLine("done");

// show the metrics
Console.WriteLine();
Console.WriteLine($"Model metrics:");
Console.WriteLine($"  RMSE: {metrics.Rms:#.##}");
Console.WriteLine($"  L1:   {metrics.L1:#.##}");
Console.WriteLine($"  L2:   {metrics.L2:#.##}");
Console.WriteLine();