Adding binary saving and loading to MLContext.Data (#1678)

* Adding binary saving and loading to MLContext.Data

* Addressing PR comments

* Adding ReadFromBinary extensions to read from both a stream and from a file

Author: najeeb-kazmi

src/Microsoft.ML.Data/DataLoadSave/Binary/BinaryLoaderSaverCatalog.cs

@@ -0,0 +1,65 @@
+// 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 System.IO;
+using Microsoft.ML.Runtime;
+using Microsoft.ML.Runtime.Data;
+using Microsoft.ML.Runtime.Data.IO;
+
+namespace Microsoft.ML
+{
+    public static class BinaryLoaderSaverCatalog
+    {
+        /// <summary>
+        /// Read a data view from a Stream on a binary file using <see cref="BinaryLoader"/>.
+        /// </summary>
+        /// <param name="catalog">The catalog.</param>
+        /// <param name="stream">The stream to read from.</param>
+        public static IDataView ReadFromBinary(this DataOperations catalog, Stream stream)
+        {
+            Contracts.CheckValue(stream, nameof(stream));
+
+            var env = catalog.GetEnvironment();
+
+            var reader = new BinaryLoader(env, new BinaryLoader.Arguments(), stream);
+            return reader;
+        }
+
+        /// <summary>
+        /// Read a data view from a binary file using <see cref="BinaryLoader"/>.
+        /// </summary>
+        /// <param name="catalog">The catalog.</param>
+        /// <param name="path">The path to the file to read from.</param>
+        public static IDataView ReadFromBinary(this DataOperations catalog, string path)
+        {
+            Contracts.CheckNonEmpty(path, nameof(path));
+
+            var env = catalog.GetEnvironment();
+
+            var reader = new BinaryLoader(env, new BinaryLoader.Arguments(), path);
+            return reader;
+        }
+
+        /// <summary>
+        /// Save the data view into a binary stream.
+        /// </summary>
+        /// <param name="catalog">The catalog.</param>
+        /// <param name="data">The data view to save.</param>
+        /// <param name="stream">The stream to write to.</param>
+        /// <param name="keepHidden">Whether to keep hidden columns in the dataset.</param>
+        public static void SaveAsBinary(this DataOperations catalog, IDataView data, Stream stream,
+            bool keepHidden = false)
+        {
+            Contracts.CheckValue(catalog, nameof(catalog));
+            Contracts.CheckValue(data, nameof(data));
+            Contracts.CheckValue(stream, nameof(stream));
+
+            var env = catalog.GetEnvironment();
+            var saver = new BinarySaver(env, new BinarySaver.Arguments());
+
+            using (var ch = env.Start("Saving data"))
+                DataSaverUtils.SaveDataView(ch, saver, data, stream, keepHidden);
+        }
+    }
+}