adding docs and made constructors internal

Author: artidoro

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

@@ -86,15 +86,15 @@ private static VersionInfo GetVersionInfo()
         /// <summary>
         /// Create a <see cref="KeyToValueMappingTransformer"/> that takes and transforms one column.
         /// </summary>
-        public KeyToValueMappingTransformer(IHostEnvironment env, string columnName)
+        internal KeyToValueMappingTransformer(IHostEnvironment env, string columnName)
             : this(env, (columnName, columnName))
         {
         }
 
         /// <summary>
         /// Create a <see cref="KeyToValueMappingTransformer"/> that takes multiple pairs of columns.
         /// </summary>
-        public KeyToValueMappingTransformer(IHostEnvironment env, params (string outputColumnName, string inputColumnName)[] columns)
+        internal KeyToValueMappingTransformer(IHostEnvironment env, params (string outputColumnName, string inputColumnName)[] columns)
             : base(Contracts.CheckRef(env, nameof(env)).Register(nameof(KeyToValueMappingTransformer)), columns)
         {
         }
@@ -516,6 +516,10 @@ internal KeyToValueMappingEstimator(IHostEnvironment env, params (string outputC
         {
         }
 
+        /// <summary>
+        /// Returns the shape of the schema which will be produced by the transformer.
+        /// Used for schema propagation and verification in a pipeline.
+        /// </summary>
         public override SchemaShape GetOutputSchema(SchemaShape inputSchema)
         {
             Host.CheckValue(inputSchema, nameof(inputSchema));

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

@@ -105,8 +105,15 @@ internal ValueToKeyMappingEstimator(IHostEnvironment env, ColumnInfo[] columns,
             _keyData = keyData;
         }
 
+        /// <summary>
+        /// Fit to the <paramref name="input"/> data and build the dictionaries used for mapping.
+        /// </summary>
         public ValueToKeyMappingTransformer Fit(IDataView input) => new ValueToKeyMappingTransformer(_host, input, _columns, _keyData, false);
 
+        /// <summary>
+        /// Returns the shape of the schema which will be produced by the transformer.
+        /// Used for schema propagation and verification in a pipeline.
+        /// </summary>
         public SchemaShape GetOutputSchema(SchemaShape inputSchema)
         {
             _host.CheckValue(inputSchema, nameof(inputSchema));

src/Microsoft.ML.Transforms/OneHotEncoding.cs

@@ -275,6 +275,10 @@ internal OneHotEncodingEstimator(IHostEnvironment env, ColumnInfo[] columns, IDa
             }
         }
 
+        /// <summary>
+        /// Returns the shape of the schema which will be produced by the transformer.
+        /// Used for schema propagation and verification in a pipeline.
+        /// </summary>
         public SchemaShape GetOutputSchema(SchemaShape inputSchema)
         {
             if (_toSomething != null)