Remove append calls since they not compatible with 4.6 framework (#2643)

Author: Ivanidzo4ka

src/Microsoft.ML.Data/Training/TrainerUtils.cs

@@ -228,17 +228,17 @@ public static void CheckOptGroup(this RoleMappedData data)
             Contracts.AssertValueOrNull(extraCols);
 
             var columns = extraCols == null ?
-                Enumerable.Empty<DataViewSchema.Column>() :
-                data.Data.Schema.Where(c => extraCols.Contains(c.Index));
+                new List<DataViewSchema.Column>() :
+                data.Data.Schema.Where(c => extraCols.Contains(c.Index)).ToList();
 
             if ((opt & CursOpt.Label) != 0 && data.Schema.Label.HasValue)
-                columns = columns.Append(data.Schema.Label.Value);
+                columns.Add(data.Schema.Label.Value);
             if ((opt & CursOpt.Features) != 0 && data.Schema.Feature.HasValue)
-                columns = columns.Append(data.Schema.Feature.Value);
+                columns.Add(data.Schema.Feature.Value);
             if ((opt & CursOpt.Weight) != 0 && data.Schema.Weight.HasValue)
-                columns = columns.Append(data.Schema.Weight.Value);
+                columns.Add(data.Schema.Weight.Value);
             if ((opt & CursOpt.Group) != 0 && data.Schema.Group.HasValue)
-                columns = columns.Append(data.Schema.Group.Value);
+                columns.Add(data.Schema.Group.Value);
             return columns;
         }
 

src/Microsoft.ML.StandardLearners/FactorizationMachine/FactorizationMachineTrainer.cs

@@ -279,9 +279,10 @@ private static double CalculateAvgLoss(IChannel ch, RoleMappedData data, bool no
             badExampleCount = 0;
             int count = 0;
 
-            var columns = featureColumns.Append(data.Schema.Label.Value);
+            var columns = new List<DataViewSchema.Column>(featureColumns);
+            columns.Add(data.Schema.Label.Value);
             if (data.Schema.Weight != null)
-                columns.Append(data.Schema.Weight.Value);
+                columns.Add(data.Schema.Weight.Value);
 
             using (var cursor = data.Data.GetRowCursor(columns))
             {