Minor changes

Author: TomFinley

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

@@ -11,7 +11,8 @@ namespace Microsoft.ML.Runtime.Data
     /// <summary>
     /// This contains information about a column in an <see cref="IDataView"/>. It is essentially a convenience cache
     /// containing the name, column index, and column type for the column. The intended usage is that users of <see cref="RoleMappedSchema"/>
-    /// to get the column index and type associated with 
+    /// will have a convenient method of getting the index and type without having to separately query it through the <see cref="ISchema"/>,
+    /// since practically the first thing a consumer of a <see cref="RoleMappedSchema"/> will want to do once they get a mappping is
     /// </summary>
     public sealed class ColumnInfo
     {

src/Microsoft.ML.Data/Commands/TrainCommand.cs

@@ -468,16 +468,11 @@ private static List<IDataTransform> BacktrackPipe(IDataView dataPipe, out IDataV
             Contracts.AssertValue(dataPipe);
 
             var transforms = new List<IDataTransform>();
-            while (true)
+            while (dataPipe is IDataTransform xf)
             {
                 // REVIEW: a malicious user could construct a loop in the Source chain, that would
                 // cause this method to iterate forever (and throw something when the list overflows). There's 
                 // no way to insulate from ALL malicious behavior.
-
-                var xf = dataPipe as IDataTransform;
-                if (xf == null)
-                    break;
-
                 transforms.Add(xf);
                 dataPipe = xf.Source;
                 Contracts.AssertValue(dataPipe);