Fix creation of dataviews inferred with .NET types with sparse vectors (dotnet#587)

`DataViewConstructionUtils`'s methods to create dataviews over .NET types will now have correctly inferred "getters" in the case of sparse vectors.

Author: xadupre

src/Microsoft.ML.Api/DataViewConstructionUtils.cs

@@ -198,6 +198,7 @@ private Delegate CreateGetter(int index)
                         Ch.Assert(outputType.GetGenericTypeDefinition() == typeof(VBuffer<>));
                         Ch.Assert(outputType.GetGenericArguments()[0] == colType.ItemType.RawType);
                         del = CreateDirectVBufferGetterDelegate<int>;
+                        genericType = colType.ItemType.RawType;
                     }
                     else if (colType.IsPrimitive)
                     {

src/Microsoft.ML.Api/TypedCursor.cs

@@ -349,6 +349,7 @@ private Action<TRow> GenerateSetter(IRow input, int index, InternalSchemaDefinit
                     Ch.Assert(fieldType.GetGenericTypeDefinition() == typeof(VBuffer<>));
                     Ch.Assert(fieldType.GetGenericArguments()[0] == colType.ItemType.RawType);
                     del = CreateVBufferToVBufferSetter<int>;
+                    genericType = colType.ItemType.RawType;
                 }
                 else if (colType.IsPrimitive)
                 {

test/Microsoft.ML.TestFramework/TestSparseDataView.cs

@@ -0,0 +1,116 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.ML.Runtime.Api;
+using Microsoft.ML.Runtime.Data;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Microsoft.ML.Runtime.RunTests
+{
+    public sealed class TestSparseDataView : TestDataViewBase
+    {
+        private const string Cat = "DataView";
+
+        public TestSparseDataView(ITestOutputHelper obj) : base(obj)
+        {
+        }
+
+        private class DenseExample<T>
+        {
+            [VectorType(2)]
+            public T[] X;
+        }
+
+        private class SparseExample<T>
+        {
+            [VectorType(5)]
+            public VBuffer<T> X;
+        }
+
+        [Fact]
+        [TestCategory(Cat)]
+        public void SparseDataView()
+        {
+            GenericSparseDataView(new[] { 1f, 2f, 3f }, new[] { 1f, 10f, 100f });
+            GenericSparseDataView(new DvInt4[] { 1, 2, 3 }, new DvInt4[] { 1, 10, 100 });
+            GenericSparseDataView(new DvBool[] { true, true, true }, new DvBool[] { false, false, false });
+            GenericSparseDataView(new double[] { 1, 2, 3 }, new double[] { 1, 10, 100 });
+            GenericSparseDataView(new DvText[] { new DvText("a"), new DvText("b"), new DvText("c") },
+                                  new DvText[] { new DvText("aa"), new DvText("bb"), new DvText("cc") });
+        }
+
+        private void GenericSparseDataView<T>(T[] v1, T[] v2)
+        {
+            var inputs = new[] {
+                new SparseExample<T>() { X = new VBuffer<T> (5, 3, v1, new int[] { 0, 2, 4 }) },
+                new SparseExample<T>() { X = new VBuffer<T> (5, 3, v2, new int[] { 0, 1, 3 }) }
+            };
+            using (var host = new TlcEnvironment())
+            {
+                var data = host.CreateStreamingDataView(inputs);
+                var value = new VBuffer<T>();
+                int n = 0;
+                using (var cur = data.GetRowCursor(i => true))
+                {
+                    var getter = cur.GetGetter<VBuffer<T>>(0);
+                    while (cur.MoveNext())
+                    {
+                        getter(ref value);
+                        Assert.True(value.Count == 3);
+                        ++n;
+                    }
+                }
+                Assert.True(n == 2);
+                var iter = data.AsEnumerable<SparseExample<T>>(host, false).GetEnumerator();
+                n = 0;
+                while (iter.MoveNext())
+                    ++n;
+                Assert.True(n == 2);
+            }
+        }
+
+        [Fact]
+        [TestCategory(Cat)]
+        public void DenseDataView()
+        {
+            GenericDenseDataView(new[] { 1f, 2f, 3f }, new[] { 1f, 10f, 100f });
+            GenericDenseDataView(new DvInt4[] { 1, 2, 3 }, new DvInt4[] { 1, 10, 100 });
+            GenericDenseDataView(new DvBool[] { true, true, true }, new DvBool[] { false, false, false });
+            GenericDenseDataView(new double[] { 1, 2, 3 }, new double[] { 1, 10, 100 });
+            GenericDenseDataView(new DvText[] { new DvText("a"), new DvText("b"), new DvText("c") },
+                                 new DvText[] { new DvText("aa"), new DvText("bb"), new DvText("cc") });
+        }
+
+        private void GenericDenseDataView<T>(T[] v1, T[] v2)
+        {
+            var inputs = new[] {
+                new DenseExample<T>() { X = v1 },
+                new DenseExample<T>() { X = v2 }
+            };
+            using (var host = new TlcEnvironment())
+            {
+                var data = host.CreateStreamingDataView(inputs);
+                var value = new VBuffer<T>();
+                int n = 0;
+                using (var cur = data.GetRowCursor(i => true))
+                {
+                    var getter = cur.GetGetter<VBuffer<T>>(0);
+                    while (cur.MoveNext())
+                    {
+                        getter(ref value);
+                        Assert.True(value.Count == 3);
+                        ++n;
+                    }
+                }
+                Assert.True(n == 2);
+                var iter = data.AsEnumerable<DenseExample<T>>(host, false).GetEnumerator();
+                n = 0;
+                while (iter.MoveNext())
+                    ++n;
+                Assert.True(n == 2);
+            }
+        }
+    }
+}