Fix SupportedMetric.ByName() method (dotnet#280)

* Fix for SupportedMetric.ByName() method. Include new unit test for function.

* Fix for SupportedMetric.ByName() method. Include new unit test for function.

* Fix for SupportedMetric.ByName() method. Include new unit test for function.

* Removed unnecessary field filter, per review comment.

Author: george-microsoft

src/Microsoft.ML.PipelineInference/AutoInference.cs

@@ -98,12 +98,13 @@ private SupportedMetric(string name, bool isMaximizing)
             public static SupportedMetric ByName(string name)
             {
                 var fields =
-                    typeof(SupportedMetric).GetMembers(BindingFlags.Static | BindingFlags.Public)
-                    .Where(s => s.MemberType == MemberTypes.Field);
+                    typeof(SupportedMetric).GetFields(BindingFlags.Static | BindingFlags.Public);
+
                 foreach (var field in fields)
                 {
-                    if (name.Equals(field.Name, StringComparison.OrdinalIgnoreCase))
-                        return (SupportedMetric)typeof(SupportedMetric).GetField(field.Name).GetValue(null);
+                    var metric = (SupportedMetric)field.GetValue(Auc);
+                    if (name.Equals(metric.Name, StringComparison.OrdinalIgnoreCase))
+                        return metric;
                 }
                 throw new NotSupportedException($"Metric '{name}' not supported.");
             }

test/Microsoft.ML.Predictor.Tests/TestAutoInference.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Linq;
+using System.Collections.Generic;
 using Newtonsoft.Json.Linq;
 using Microsoft.ML.Runtime.Data;
 using Microsoft.ML.Runtime.EntryPoints;
@@ -411,6 +412,27 @@ public void TestPipelineNodeCloning()
             }
         }
 
+        [Fact]
+        public void TestSupportedMetricsByName()
+        {
+            var names = new List<string>()
+            {
+                AutoInference.SupportedMetric.AccuracyMacro.Name,
+                AutoInference.SupportedMetric.AccuracyMicro.Name,
+                AutoInference.SupportedMetric.Auc.Name,
+                AutoInference.SupportedMetric.AuPrc.Name,
+                AutoInference.SupportedMetric.Dbi.Name,
+                AutoInference.SupportedMetric.F1.Name,
+                AutoInference.SupportedMetric.LogLossReduction.Name
+            };
+
+            foreach (var name in names)
+            {
+                var metric = AutoInference.SupportedMetric.ByName(name);
+                Assert.Equal(metric.Name, name);
+            }
+        }
+
         [Fact]
         public void TestHyperparameterFreezing()
         {