PR feedback.

src/DefaultGenApiDocIds.txt

@@ -0,0 +1,3 @@
+// These attributes should be excluded from reference assemblies.
+
+T:Microsoft.ML.BestFriendAttribute

src/Directory.Build.props

@@ -31,6 +31,7 @@
          API missing from old) -->
     <RunApiCompatForSrc>true</RunApiCompatForSrc>
     <RunMatchingRefApiCompat>false</RunMatchingRefApiCompat>
+    <ApiCompatExcludeAttributeList>$(MSBuildThisFileDirectory)DefaultGenApiDocIds.txt</ApiCompatExcludeAttributeList>
   </PropertyGroup>
 
   <ItemGroup>

src/Microsoft.ML.Data/Transforms/Hashing.cs

@@ -1134,7 +1134,7 @@ internal static class Defaults
         }
 
         /// <summary>
-        /// Describes how the transformer handles one column pair.
+        /// Initializes a new instance of the ColumnOptions class.
         /// </summary>
         public sealed class ColumnOptions
         {
@@ -1163,9 +1163,6 @@ public sealed class ColumnOptions
             /// </summary>
             public int MaximumNumberOfInverts { get; set; }
 
-            /// <summary>
-            /// Describes how the transformer handles one column pair.
-            /// </summary>
             /// <param name="name">Name of the column resulting from the transformation of <paramref name="inputColumnName"/>.</param>
             /// <param name="inputColumnName">Name of column to transform. If set to <see langword="null"/>, the value of the <paramref name="name"/> will be used as source.</param>
             /// <param name="numberOfBits">Number of bits to hash into. Must be between 1 and 31, inclusive.</param>
@@ -1189,6 +1186,10 @@ public ColumnOptions(string name,
                 UseOrderedHashing = useOrderedHashing;
                 MaximumNumberOfInverts = maximumNumberOfInverts;
             }
+
+            public ColumnOptions()
+            {
+            }
         }
 
         /// <summary>

test/Microsoft.ML.Functional.Tests/DataTransformation.cs

@@ -9,6 +9,7 @@
 using Microsoft.ML.Transforms.Text;
 using Xunit;
 using Xunit.Abstractions;
+using static Microsoft.ML.Transforms.HashingEstimator;
 
 namespace Microsoft.ML.Functional.Tests
 {
@@ -185,6 +186,35 @@ void ExtensibilityNormalizeColumns()
                     Assert.InRange(row.Features[i], -1, 1);
         }
 
+        [Fact]
+        void HashColumns()
+        {
+            // Concurrency must be 1 to assure that the mapping is done sequentially.
+            var mlContext = new MLContext(seed: 1);
+
+            // Load the Iris dataset.
+            var data = mlContext.Data.LoadFromTextFile<Iris>(
+                TestCommon.GetDataPath(DataDir, TestDatasets.iris.trainFilename),
+                hasHeader: TestDatasets.iris.fileHasHeader,
+                separatorChar: TestDatasets.iris.fileSeparator);
+
+            // Compose the transformation.
+            var pipeline = mlContext.Transforms.Concatenate("Features", Iris.Features)
+                .Append(mlContext.Transforms.Conversion.Hash(new[] {
+                    new ColumnOptions() {
+                        Name = "Features", InputColumnName = "Features", NumberOfBits =  31, UseOrderedHashing = true } }));
+
+            // Transform the data.
+            var transformedData = pipeline.Fit(data).Transform(data);
+
+            // Validate that the data was normalized to between -1 and 1.
+            var dataEnumerator = mlContext.Data.CreateEnumerable<HashedFeatureColumn>(transformedData, true);
+            foreach (var row in dataEnumerator)
+                // Verify per-slot normalization.
+                for (int i = 0; i < row.Features.Length; i++)
+                    Assert.InRange(row.Features[i], (uint)0, (uint)Math.Pow(2, 31));
+        }
+
         private float GetRandomNumber(float number)
         {
             var seed = (int)(10 * number);

test/Microsoft.ML.Functional.Tests/Datasets/CommonColumns.cs

@@ -12,6 +12,11 @@ internal sealed class FeatureColumn
         public float[] Features { get; set; }
     }
 
+    internal sealed class HashedFeatureColumn
+    {
+        public uint[] Features { get; set; }
+    }
+
     /// <summary>
     /// A class to hold the output of FeatureContributionCalculator
     /// </summary>