Replace predicate with an IEnumerable<DataViewSchema.Column> for IRowToRowMapper.GetRow and ISchemaBoundRowMapper.GetRow

src/Microsoft.Data.DataView/DataViewSchema.cs

@@ -217,14 +217,14 @@ private void CheckGetter<TValue>(Delegate getter)
             /// <summary>
             /// Get a getter delegate for one value of the annotations row.
             /// </summary>
-            public ValueGetter<TValue> GetGetter<TValue>(int col)
+            public ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column column)
             {
-                if (!(0 <= col && col < Schema.Count))
-                    throw new ArgumentOutOfRangeException(nameof(col));
-                var typedGetter = _getters[col] as ValueGetter<TValue>;
+                if (column.Index >= _getters.Length)
+                    throw new ArgumentException(nameof(column));
+                var typedGetter = _getters[column.Index] as ValueGetter<TValue>;
                 if (typedGetter == null)
                 {
-                    Debug.Assert(_getters[col] != null);
+                    Debug.Assert(_getters[column.Index] != null);
                     throw new InvalidOperationException($"Invalid call to '{nameof(GetGetter)}'");
                 }
                 return typedGetter;
@@ -238,7 +238,7 @@ public void GetValue<TValue>(string kind, ref TValue value)
                 var column = Schema.GetColumnOrNull(kind);
                 if (column == null)
                     throw new InvalidOperationException($"Invalid call to '{nameof(GetValue)}'");
-                GetGetter<TValue>(column.Value.Index)(ref value);
+                GetGetter<TValue>(column.Value)(ref value);
             }
 
             public override string ToString() => string.Join(", ", Schema.Select(x => x.Name));

src/Microsoft.Data.DataView/IDataView.cs

@@ -134,14 +134,16 @@ public abstract class DataViewRow : IDisposable
         /// <summary>
         /// Returns whether the given column is active in this row.
         /// </summary>
-        public abstract bool IsColumnActive(int col);
+        public abstract bool IsColumnActive(DataViewSchema.Column column);
 
         /// <summary>
-        /// Returns a value getter delegate to fetch the given column value from the row.
+        /// Returns a value getter delegate to fetch the value of the given <paramref name="column"/>, from the row.
         /// This throws if the column is not active in this row, or if the type
         /// <typeparamref name="TValue"/> differs from this column's type.
         /// </summary>
-        public abstract ValueGetter<TValue> GetGetter<TValue>(int col);
+        /// <typeparam name="TValue"> is the column's content type.</typeparam>
+        /// <param name="column"> is the output column whose getter should be returned.</param>
+        public abstract ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column column);
 
         /// <summary>
         /// Gets a <see cref="Schema"/>, which provides name and type information for variables

src/Microsoft.Data.DataView/SchemaDebuggerProxy.cs

@@ -41,16 +41,16 @@ private static List<KeyValuePair<string, object>> BuildValues(DataViewSchema.Ann
             foreach (var column in annotations.Schema)
             {
                 var name = column.Name;
-                var value = Utils.MarshalInvoke(GetValue<int>, column.Type.RawType, annotations, column.Index);
+                var value = Utils.MarshalInvoke(GetValue<DataViewSchema.Column>, column.Type.RawType, annotations, column);
                 result.Add(new KeyValuePair<string, object>(name, value));
             }
             return result;
         }
 
-        private static object GetValue<T>(DataViewSchema.Annotations annotations, int columnIndex)
+        private static object GetValue<T>(DataViewSchema.Annotations annotations, DataViewSchema.Column column)
         {
             T value = default;
-            annotations.GetGetter<T>(columnIndex)(ref value);
+            annotations.GetGetter<T>(column)(ref value);
             return value;
         }
     }

src/Microsoft.ML.Core/Data/AnnotationUtils.cs

@@ -460,9 +460,22 @@ public AnnotationRow(DataViewSchema.Annotations annotations)
             public override DataViewSchema Schema => _annotations.Schema;
             public override long Position => 0;
             public override long Batch => 0;
-            public override ValueGetter<TValue> GetGetter<TValue>(int col) => _annotations.GetGetter<TValue>(col);
+
+            /// <summary>
+            /// Returns a value getter delegate to fetch the value of column with the given columnIndex, from the row.
+            /// This throws if the column is not active in this row, or if the type
+            /// <typeparamref name="TValue"/> differs from this column's type.
+            /// </summary>
+            /// <typeparam name="TValue"> is the column's content type.</typeparam>
+            /// <param name="column"> is the output column whose getter should be returned.</param>
+            public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column column) => _annotations.GetGetter<TValue>(column);
+
             public override ValueGetter<DataViewRowId> GetIdGetter() => (ref DataViewRowId dst) => dst = default;
-            public override bool IsColumnActive(int col) => true;
+
+            /// <summary>
+            /// Returns whether the given column is active in this row.
+            /// </summary>
+            public override bool IsColumnActive(DataViewSchema.Column column) => true;
         }
 
         /// <summary>

src/Microsoft.ML.Core/Data/IRowToRowMapper.cs

@@ -35,8 +35,7 @@ public interface IRowToRowMapper
 
         /// <summary>
         /// Get an <see cref="DataViewRow"/> with the indicated active columns, based on the input <paramref name="input"/>.
-        /// The active columns are those for which <paramref name="active"/> returns true. Getting values on inactive
-        /// columns of the returned row will throw. Null predicates are disallowed.
+        /// Getting values on inactive columns of the returned row will throw.
         ///
         /// The <see cref="DataViewRow.Schema"/> of <paramref name="input"/> should be the same object as
         /// <see cref="InputSchema"/>. Implementors of this method should throw if that is not the case. Conversely,
@@ -48,6 +47,6 @@ public interface IRowToRowMapper
         /// The output <see cref="DataViewRow"/> values are re-computed when requested through the getters. Also, the returned
         /// <see cref="DataViewRow"/> will dispose <paramref name="input"/> when it is disposed.
         /// </summary>
-        DataViewRow GetRow(DataViewRow input, Func<int, bool> active);
+        DataViewRow GetRow(DataViewRow input, IEnumerable<DataViewSchema.Column> activeColumns);
     }
 }

src/Microsoft.ML.Core/Data/ISchemaBindableMapper.cs

@@ -73,8 +73,7 @@ internal interface ISchemaBoundRowMapper : ISchemaBoundMapper
 
         /// <summary>
         /// Get an <see cref="DataViewRow"/> with the indicated active columns, based on the input <paramref name="input"/>.
-        /// The active columns are those for which <paramref name="active"/> returns true. Getting values on inactive
-        /// columns of the returned row will throw. Null predicates are disallowed.
+        /// Getting values on inactive columns of the returned row will throw.
         ///
         /// The <see cref="DataViewRow.Schema"/> of <paramref name="input"/> should be the same object as
         /// <see cref="InputSchema"/>. Implementors of this method should throw if that is not the case. Conversely,
@@ -86,6 +85,6 @@ internal interface ISchemaBoundRowMapper : ISchemaBoundMapper
         /// The output <see cref="DataViewRow"/> values are re-computed when requested through the getters. Also, the returned
         /// <see cref="DataViewRow"/> will dispose <paramref name="input"/> when it is disposed.
         /// </summary>
-        DataViewRow GetRow(DataViewRow input, Func<int, bool> active);
+        DataViewRow GetRow(DataViewRow input, IEnumerable<DataViewSchema.Column> activeColumns);
     }
 }

src/Microsoft.ML.Core/Data/LinkedRowRootCursorBase.cs

@@ -9,7 +9,7 @@ namespace Microsoft.ML.Data
     /// <summary>
     /// A base class for a <see cref="DataViewRowCursor"/> that has an input cursor, but still needs to do work on
     /// <see cref="DataViewRowCursor.MoveNext"/>. Note that the default
-    /// <see cref="LinkedRowRootCursorBase.GetGetter{TValue}(int)"/> assumes that each input column is exposed as an
+    /// <see cref="LinkedRowRootCursorBase.GetGetter{TValue}(DataViewSchema.Column)"/> assumes that each input column is exposed as an
     /// output column with the same column index.
     /// </summary>
     [BestFriend]
@@ -29,15 +29,25 @@ protected LinkedRowRootCursorBase(IChannelProvider provider, DataViewRowCursor i
             Schema = schema;
         }
 
-        public sealed override bool IsColumnActive(int col)
+        /// <summary>
+        /// Returns whether the given column is active in this row.
+        /// </summary>
+        public sealed override bool IsColumnActive(DataViewSchema.Column column)
         {
-            Ch.Check(0 <= col && col < Schema.Count);
-            return _active == null || _active[col];
+            Ch.Check(column.Index < Schema.Count);
+            return _active == null || _active[column.Index];
         }
 
-        public override ValueGetter<TValue> GetGetter<TValue>(int col)
+        /// <summary>
+        /// Returns a value getter delegate to fetch the value of column with the given columnIndex, from the row.
+        /// This throws if the column is not active in this row, or if the type
+        /// <typeparamref name="TValue"/> differs from this column's type.
+        /// </summary>
+        /// <typeparam name="TValue"> is the column's content type.</typeparam>
+        /// <param name="column"> is the output column whose getter should be returned.</param>
+        public override ValueGetter<TValue> GetGetter<TValue>(DataViewSchema.Column column)
         {
-            return Input.GetGetter<TValue>(col);
+            return Input.GetGetter<TValue>(column);
         }
     }
 }

src/Microsoft.ML.Core/Utilities/Utils.cs

@@ -776,6 +776,41 @@ public static T[] BuildArray<T>(int length, Func<int, T> func)
             return result;
         }
 
+        /// <summary>
+        /// Given a predicate, over a range of values defined by a limit calculate
+        /// first the values for which that predicate was true, and second an inverse
+        /// map.
+        /// </summary>
+        /// <param name="schema">The input schema where the predicate can check if columns are active.</param>
+        /// <param name="pred">The predicate to test for various value</param>
+        /// <param name="map">An ascending array of values from 0 inclusive
+        /// to <paramref name="schema.Count"/> exclusive, holding all values for which
+        /// <paramref name="pred"/> is true</param>
+        /// <param name="invMap">Forms an inverse mapping of <paramref name="map"/>,
+        /// so that <c><paramref name="invMap"/>[<paramref name="map"/>[i]] == i</c>,
+        /// and for other entries not appearing in <paramref name="map"/>,
+        /// <c><paramref name="invMap"/>[i] == -1</c></param>
+        public static void BuildSubsetMaps(DataViewSchema schema, Func<DataViewSchema.Column, bool> pred, out int[] map, out int[] invMap)
+        {
+            Contracts.CheckValue(schema, nameof(schema));
+            Contracts.Check(schema.Count > 0, nameof(schema));
+            Contracts.CheckValue(pred, nameof(pred));
+            // REVIEW: Better names?
+            List<int> mapList = new List<int>();
+            invMap = new int[schema.Count];
+            for (int c = 0; c < schema.Count; ++c)
+            {
+                if (!pred(schema[c]))
+                {
+                    invMap[c] = -1;
+                    continue;
+                }
+                invMap[c] = mapList.Count;
+                mapList.Add(c);
+            }
+            map = mapList.ToArray();
+        }
+
         /// <summary>
         /// Given a predicate, over a range of values defined by a limit calculate
         /// first the values for which that predicate was true, and second an inverse