update cookbooks and added comments about laziness of load

Author: artidoro

docs/code/MlNetCookBook.md

@@ -37,7 +37,7 @@ public static void FeatureSelectionTransform()
                     ),
                 separator: '\t', hasHeader: true);
 
-            // Then, we use the reader to load the data as an IDataView.
+            // Then, we use the loader to load the data as an IDataView.
             var data = loader.Load(dataFilePath);
 
             // Second, we define the transformations that we apply on the data. Remember that an Estimator does not transform data

docs/code/experimental/MlNetCookBookStaticApi.md

@@ -12,7 +12,8 @@ namespace Microsoft.ML
     public static class BinaryLoaderSaverCatalog
     {
         /// <summary>
-        /// Load a data view from an <see cref="IMultiStreamSource"/> on a binary file.
+        /// Load a <see cref="IDataView"/> from an <see cref="IMultiStreamSource"/> on a binary file.
+        /// Note that <see cref="IDataView"/>'s are lazy, so no actual loading happens here, just schema validation.
         /// </summary>
         /// <param name="catalog">The catalog.</param>
         /// <param name="fileSource">The file source to load from. This can be a <see cref="MultiFileSource"/>, for example.</param>
@@ -27,7 +28,8 @@ public static IDataView LoadFromBinary(this DataOperationsCatalog catalog, IMult
         }
 
         /// <summary>
-        /// Load a data view from a binary file.
+        /// Load a <see cref="IDataView"/> from a binary file.
+        /// Note that <see cref="IDataView"/>'s are lazy, so no actual loading happens here, just schema validation.
         /// </summary>
         /// <param name="catalog">The catalog.</param>
         /// <param name="path">The path to the file to load from.</param>
@@ -42,7 +44,7 @@ public static IDataView LoadFromBinary(this DataOperationsCatalog catalog, strin
         }
 
         /// <summary>
-        /// Save the data view into a binary stream.
+        /// Save the <see cref="IDataView"/> into a binary stream.
         /// </summary>
         /// <param name="catalog">The catalog.</param>
         /// <param name="data">The data view to save.</param>

docs/samples/Microsoft.ML.Samples/Static/FeatureSelectionTransform.cs

@@ -33,6 +33,10 @@ public CompositeDataLoader(IDataLoader<TSource> loader, TransformerChain<TLastTr
             Transformer = transformerChain ?? new TransformerChain<TLastTransformer>();
         }
 
+        /// <summary>
+        /// Produce the data view from the specified input.
+        /// Note that <see cref="IDataView"/>'s are lazy, so no actual loading happens here, just schema validation.
+        /// </summary>
         public IDataView Load(TSource input)
         {
             var idv = Loader.Load(input);

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

@@ -10,11 +10,12 @@ namespace Microsoft.ML
     public static class DataLoaderExtensions
     {
         /// <summary>
-        /// Reads data from one or more file <paramref name="path"/> into an <see cref="IDataView"/>.
+        /// Loads data from one or more file <paramref name="path"/> into an <see cref="IDataView"/>.
+        /// Note that <see cref="IDataView"/>'s are lazy, so no actual loading happens here, just schema validation.
         /// </summary>
         /// <param name="loader">The loader to use.</param>
         /// <param name="path">One or more paths from which to load data.</param>
         public static IDataView Load(this IDataLoader<IMultiStreamSource> loader, params string[] path)
             => loader.Load(new MultiFileSource(path));
     }
-}
+}

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

@@ -82,7 +82,8 @@ public static TextLoader CreateTextLoader<TInput>(this DataOperationsCatalog cat
                 allowSparse, trimWhitespace, dataSample: dataSample);
 
         /// <summary>
-        /// Load a data view from a text file using <see cref="TextLoader"/>.
+        /// Load a <see cref="IDataView"/> from a text file using <see cref="TextLoader"/>.
+        /// Note that <see cref="IDataView"/>'s are lazy, so no actual loading happens here, just schema validation.
         /// </summary>
         /// <param name="catalog">The <see cref="DataOperationsCatalog"/> catalog.</param>
         /// <param name="path">The path to the file.</param>
@@ -119,7 +120,8 @@ public static IDataView LoadFromTextFile(this DataOperationsCatalog catalog,
         }
 
         /// <summary>
-        /// Load a data view from a text file using <see cref="TextLoader"/>.
+        /// Load a <see cref="IDataView"/> from a text file using <see cref="TextLoader"/>.
+        /// Note that <see cref="IDataView"/>'s are lazy, so no actual loading happens here, just schema validation.
         /// </summary>
         /// <param name="catalog">The <see cref="DataOperationsCatalog"/> catalog.</param>
         /// <param name="path">The path to the file.</param>
@@ -152,7 +154,8 @@ public static IDataView LoadFromTextFile<TInput>(this DataOperationsCatalog cata
         }
 
         /// <summary>
-        /// Load a data view from a text file using <see cref="TextLoader"/>.
+        /// Load a <see cref="IDataView"/> from a text file using <see cref="TextLoader"/>.
+        /// Note that <see cref="IDataView"/>'s are lazy, so no actual loading happens here, just schema validation.
         /// </summary>
         /// <param name="catalog">The <see cref="DataOperationsCatalog"/> catalog.</param>
         /// <param name="path">Specifies a file from which to load.</param>
@@ -169,7 +172,7 @@ public static IDataView LoadFromTextFile(this DataOperationsCatalog catalog, str
         }
 
         /// <summary>
-        /// Save the data view as text.
+        /// Save the <see cref="IDataView"/> as text.
         /// </summary>
         /// <param name="catalog">The <see cref="DataOperationsCatalog"/> catalog.</param>
         /// <param name="data">The data view to save.</param>