No loader on APIs for ValueToKey/OneHotEncoding (#2245)

* ValueToKey and OneHotEncoding use IDataView directly for side data.
* CustomStopWordsRemovingTransform becomes transformer.
* Rename termData to keyData per Ivan.

Author: TomFinley

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

@@ -199,13 +199,13 @@ public ColumnSelectingTransformer(IHostEnvironment env, string[] keepColumns, st
             _host.CheckValueOrNull(keepColumns);
             _host.CheckValueOrNull(dropColumns);
 
-            bool keepValid = keepColumns != null && keepColumns.Count() > 0;
-            bool dropValid = dropColumns != null && dropColumns.Count() > 0;
+            bool keepValid = Utils.Size(keepColumns) > 0;
+            bool dropValid = Utils.Size(dropColumns) > 0;
 
             // Check that both are not valid
-            _host.Check(!(keepValid && dropValid), "Both keepColumns and dropColumns are set, only one can be specified.");
+            _host.Check(!(keepValid && dropValid), "Both " + nameof(keepColumns) + " and " + nameof(dropColumns) + " are set. Exactly one can be specified.");
             // Check that both are invalid
-            _host.Check(!(!keepValid && !dropValid), "Neither keepColumns or dropColumns is set, one must be specified.");
+            _host.Check(!(!keepValid && !dropValid), "Neither " + nameof(keepColumns) + " and " + nameof(dropColumns) + " is set. Exactly one must be specified.");
 
             _selectedColumns = (keepValid) ? keepColumns : dropColumns;
             KeepColumns = keepValid;
@@ -558,7 +558,7 @@ private static int[] BuildOutputToInputMap(IEnumerable<string> selectedColumns,
                     // given an input of ABC and dropping column B will result in AC.
                     // In drop mode, we drop all columns with the specified names and keep all the rest,
                     // ignoring the keepHidden argument.
-                    for(int colIdx = 0; colIdx < inputSchema.Count; colIdx++)
+                    for (int colIdx = 0; colIdx < inputSchema.Count; colIdx++)
                     {
                         if (selectedColumns.Contains(inputSchema[colIdx].Name))
                             continue;

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

@@ -112,19 +112,16 @@ public static ValueToKeyMappingEstimator MapValueToKey(this TransformsCatalog.Co
            => new ValueToKeyMappingEstimator(CatalogUtils.GetEnvironment(catalog), inputColumn, outputColumn, maxNumTerms, sort);
 
         /// <summary>
-        /// Converts value types into <see cref="KeyType"/> loading the keys to use from <paramref name="file"/>.
+        /// Converts value types into <see cref="KeyType"/>, optionally loading the keys to use from <paramref name="keyData"/>.
         /// </summary>
         /// <param name="catalog">The categorical transform's catalog.</param>
         /// <param name="columns">The data columns to map to keys.</param>
-        /// <param name="file">The path of the file containing the terms.</param>
-        /// <param name="termsColumn"></param>
-        /// <param name="loaderFactory"></param>
+        /// <param name="keyData">The data view containing the terms. If specified, this should be a single column data
+        /// view, and the key-values will be taken from taht column. If unspecified, the key-values will be determined
+        /// from the input data upon fitting.</param>
         public static ValueToKeyMappingEstimator MapValueToKey(this TransformsCatalog.ConversionTransforms catalog,
-            ValueToKeyMappingTransformer.ColumnInfo[] columns,
-            string file = null,
-            string termsColumn = null,
-            IComponentFactory<IMultiStreamSource, IDataLoader> loaderFactory = null)
-            => new ValueToKeyMappingEstimator(CatalogUtils.GetEnvironment(catalog), columns, file, termsColumn, loaderFactory);
+            ValueToKeyMappingTransformer.ColumnInfo[] columns, IDataView keyData = null)
+            => new ValueToKeyMappingEstimator(CatalogUtils.GetEnvironment(catalog), columns, keyData);
 
         /// <summary>
         /// Maps specified keys to specified values

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

@@ -9,7 +9,7 @@
 namespace Microsoft.ML.Transforms.Conversions
 {
     /// <include file='doc.xml' path='doc/members/member[@name="ValueToKeyMappingEstimator"]/*' />
-    public sealed class ValueToKeyMappingEstimator: IEstimator<ValueToKeyMappingTransformer>
+    public sealed class ValueToKeyMappingEstimator : IEstimator<ValueToKeyMappingTransformer>
     {
         public static class Defaults
         {
@@ -19,9 +19,7 @@ public static class Defaults
 
         private readonly IHost _host;
         private readonly ValueToKeyMappingTransformer.ColumnInfo[] _columns;
-        private readonly string _file;
-        private readonly string _termsColumn;
-        private readonly IComponentFactory<IMultiStreamSource, IDataLoader> _loaderFactory;
+        private readonly IDataView _keyData;
 
         /// <summary>
         /// Initializes a new instance of <see cref="ValueToKeyMappingEstimator"/>.
@@ -33,23 +31,28 @@ public static class Defaults
         /// <param name="sort">How items should be ordered when vectorized. If <see cref="ValueToKeyMappingTransformer.SortOrder.Occurrence"/> choosen they will be in the order encountered.
         /// If <see cref="ValueToKeyMappingTransformer.SortOrder.Value"/>, items are sorted according to their default comparison, for example, text sorting will be case sensitive (for example, 'A' then 'Z' then 'a').</param>
         public ValueToKeyMappingEstimator(IHostEnvironment env, string inputColumn, string outputColumn = null, int maxNumTerms = Defaults.MaxNumTerms, ValueToKeyMappingTransformer.SortOrder sort = Defaults.Sort) :
-           this(env, new [] { new ValueToKeyMappingTransformer.ColumnInfo(inputColumn, outputColumn ?? inputColumn, maxNumTerms, sort) })
+           this(env, new[] { new ValueToKeyMappingTransformer.ColumnInfo(inputColumn, outputColumn ?? inputColumn, maxNumTerms, sort) })
         {
         }
 
-        public ValueToKeyMappingEstimator(IHostEnvironment env, ValueToKeyMappingTransformer.ColumnInfo[] columns,
-            string file = null, string termsColumn = null,
-            IComponentFactory<IMultiStreamSource, IDataLoader> loaderFactory = null)
+        public ValueToKeyMappingEstimator(IHostEnvironment env, ValueToKeyMappingTransformer.ColumnInfo[] columns, IDataView keyData = null)
         {
             Contracts.CheckValue(env, nameof(env));
             _host = env.Register(nameof(ValueToKeyMappingEstimator));
+            _host.CheckNonEmpty(columns, nameof(columns));
+            _host.CheckValueOrNull(keyData);
+            if (keyData != null && keyData.Schema.Count != 1)
+            {
+                throw _host.ExceptParam(nameof(keyData), "If specified, this data view should contain only a single column " +
+                    $"containing the terms to map, but this had {keyData.Schema.Count} columns.");
+
+            }
+
             _columns = columns;
-            _file = file;
-            _termsColumn = termsColumn;
-            _loaderFactory = loaderFactory;
+            _keyData = keyData;
         }
 
-        public ValueToKeyMappingTransformer Fit(IDataView input) => new ValueToKeyMappingTransformer(_host, input, _columns, _file, _termsColumn, _loaderFactory);
+        public ValueToKeyMappingTransformer Fit(IDataView input) => new ValueToKeyMappingTransformer(_host, input, _columns, _keyData, false);
 
         public SchemaShape GetOutputSchema(SchemaShape inputSchema)
         {