Make CompositeSchema not an ISchema

1. Remove ISchema interface
2. Rename CompositeSchema to ZipBinding

Author: wschin

src/Microsoft.ML.Data/DataLoadSave/PartitionedFileLoader.cs

@@ -333,7 +333,7 @@ private Schema CreateSchema(IExceptionContext ectx, Column[] cols, IDataLoader s
                     colSchema
                 };
 
-                return Schema.Create(new CompositeSchema(schemas));
+                return new ZipBinding(schemas).OutputSchema;
             }
         }
 

src/Microsoft.ML.Data/DataView/CompositeSchema.cs

@@ -13,16 +13,16 @@ namespace Microsoft.ML.Data
     /// A convenience class for concatenating several schemas together.
     /// This would be necessary when combining IDataViews through any type of combining operation, for example, zip.
     /// </summary>
-    internal sealed class CompositeSchema : ISchema
+    internal sealed class ZipBinding
     {
         private readonly Schema[] _sources;
 
-        public Schema AsSchema { get; }
+        public Schema OutputSchema { get; }
 
         // Zero followed by cumulative column counts. Zero being used for the empty case.
         private readonly int[] _cumulativeColCounts;
 
-        public CompositeSchema(Schema[] sources)
+        public ZipBinding(Schema[] sources)
         {
             Contracts.AssertNonEmpty(sources);
             _sources = sources;
@@ -34,7 +34,11 @@ public CompositeSchema(Schema[] sources)
                 var schema = sources[i];
                 _cumulativeColCounts[i + 1] = _cumulativeColCounts[i] + schema.Count;
             }
-            AsSchema = Schema.Create(this);
+
+            var schemaBuilder = new SchemaBuilder();
+            foreach (var sourceSchema in sources)
+                schemaBuilder.AddColumns(sourceSchema);
+            OutputSchema = schemaBuilder.GetSchema();
         }
 
         public int ColumnCount => _cumulativeColCounts[_cumulativeColCounts.Length - 1];
@@ -74,50 +78,5 @@ public void GetColumnSource(int col, out int srcIndex, out int srcCol)
             srcCol = col - _cumulativeColCounts[srcIndex];
             Contracts.Assert(0 <= srcCol && srcCol < _sources[srcIndex].Count);
         }
-
-        public bool TryGetColumnIndex(string name, out int col)
-        {
-            for (int i = _sources.Length; --i >= 0;)
-            {
-                if (_sources[i].TryGetColumnIndex(name, out col))
-                {
-                    col += _cumulativeColCounts[i];
-                    return true;
-                }
-            }
-
-            col = -1;
-            return false;
-        }
-
-        public string GetColumnName(int col)
-        {
-            GetColumnSource(col, out int dv, out int srcCol);
-            return _sources[dv][srcCol].Name;
-        }
-
-        public ColumnType GetColumnType(int col)
-        {
-            GetColumnSource(col, out int dv, out int srcCol);
-            return _sources[dv][srcCol].Type;
-        }
-
-        public IEnumerable<KeyValuePair<string, ColumnType>> GetMetadataTypes(int col)
-        {
-            GetColumnSource(col, out int dv, out int srcCol);
-            return _sources[dv][srcCol].Metadata.Schema.Select(c => new KeyValuePair<string, ColumnType>(c.Name, c.Type));
-        }
-
-        public ColumnType GetMetadataTypeOrNull(string kind, int col)
-        {
-            GetColumnSource(col, out int dv, out int srcCol);
-            return _sources[dv][srcCol].Metadata.Schema.GetColumnOrNull(kind)?.Type;
-        }
-
-        public void GetMetadata<TValue>(string kind, int col, ref TValue value)
-        {
-            GetColumnSource(col, out int dv, out int srcCol);
-            _sources[dv][srcCol].Metadata.GetValue(kind, ref value);
-        }
     }
 }

src/Microsoft.ML.Data/DataView/ZipDataView.cs

@@ -25,7 +25,7 @@ public sealed class ZipDataView : IDataView
 
         private readonly IHost _host;
         private readonly IDataView[] _sources;
-        private readonly CompositeSchema _compositeSchema;
+        private readonly ZipBinding _compositeSchema;
 
         public static IDataView Create(IHostEnvironment env, IEnumerable<IDataView> sources)
         {
@@ -47,12 +47,12 @@ private ZipDataView(IHost host, IDataView[] sources)
 
             _host.Assert(Utils.Size(sources) > 1);
             _sources = sources;
-            _compositeSchema = new CompositeSchema(_sources.Select(x => x.Schema).ToArray());
+            _compositeSchema = new ZipBinding(_sources.Select(x => x.Schema).ToArray());
         }
 
         public bool CanShuffle { get { return false; } }
 
-        public Schema Schema => _compositeSchema.AsSchema;
+        public Schema Schema => _compositeSchema.OutputSchema;
 
         public long? GetRowCount()
         {
@@ -106,7 +106,7 @@ public RowCursor[] GetRowCursorSet(Func<int, bool> predicate, int n, Random rand
         private sealed class Cursor : RootCursorBase
         {
             private readonly RowCursor[] _cursors;
-            private readonly CompositeSchema _compositeSchema;
+            private readonly ZipBinding _compositeSchema;
             private readonly bool[] _isColumnActive;
             private bool _disposed;
 
@@ -172,7 +172,7 @@ protected override bool MoveManyCore(long count)
                 return true;
             }
 
-            public override Schema Schema => _compositeSchema.AsSchema;
+            public override Schema Schema => _compositeSchema.OutputSchema;
 
             public override bool IsColumnActive(int col)
             {

src/Microsoft.ML.Data/Scorers/FeatureContributionCalculation.cs

@@ -337,7 +337,7 @@ public RowMapper(IHostEnvironment env, BindableMapper parent, RoleMappedSchema s
                 }
 
                 _outputGenericSchema = _genericRowMapper.OutputSchema;
-                OutputSchema = new CompositeSchema(new Schema[] { _outputGenericSchema, _outputSchema, }).AsSchema;
+                OutputSchema = new ZipBinding(new Schema[] { _outputGenericSchema, _outputSchema, }).OutputSchema;
             }
 
             /// <summary>