Fixed bugs in OptionalColumnTransform and ColumnSelecting (#4887)

Author: harishsk

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

@@ -732,19 +732,18 @@ IDataTransform ITransformTemplate.ApplyToData(IHostEnvironment env, IDataView ne
 
             public void SaveAsOnnx(OnnxContext ctx)
             {
-                var droppedCols = new HashSet<int>(Enumerable.Range(0, InputSchema.Count));
-
                 var outputToInputMap = _mapper.OutputToInputMap;
                 for(int i = 0; i < outputToInputMap.Length; i++)
                 {
                     var srcCol = InputSchema[outputToInputMap[i]];
                     var dstCol = OutputSchema[i];
+                    if (!ctx.ContainsColumn(srcCol.Name) || dstCol.IsHidden)
+                        continue;
+
                     var srcVariable = ctx.GetVariableName(srcCol.Name);
                     var dstVariable = ctx.AddIntermediateVariable(dstCol.Type, dstCol.Name, true);
                     string opType = "Identity";
                     ctx.CreateNode(opType, srcVariable, dstVariable, ctx.GetNodeName(opType), "");
-
-                    droppedCols.Remove(srcCol.Index);
                 }
             }
         }

src/Microsoft.ML.Transforms/OptionalColumnTransform.cs

@@ -511,7 +511,12 @@ public void SaveAsOnnx(OnnxContext ctx)
                 if (!ctx.ContainsColumn(inputColumnName))
                     continue;
 
-                if (!SaveAsOnnxCore(ctx, ctx.GetVariableName(inputColumnName), _bindings.ColumnTypes[iinfo]))
+                // If there is already a column of this name, don't add this column as an OptionalColumn/Initializer
+                var srcVariableName = ctx.GetVariableName(inputColumnName);
+                if (srcVariableName != inputColumnName)
+                    continue;
+
+                if (!SaveAsOnnxCore(ctx, srcVariableName, _bindings.ColumnTypes[iinfo]))
                     ctx.RemoveColumn(inputColumnName, true);
             }
         }