[GitHub] [spark] zhengruifeng commented on a change in pull request #26547: [SPARK-29914][ML] ML models attach metadata in `transform`/`transformSchema`

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zhengruifeng commented on a change in pull request #26547: [SPARK-29914][ML] ML models attach metadata in `transform`/`transformSchema`
URL: https://github.com/apache/spark/pull/26547#discussion_r354081572
 
 

 ##########
 File path: mllib/src/main/scala/org/apache/spark/ml/feature/CountVectorizer.scala
 ##########
 @@ -326,14 +326,19 @@ class CountVectorizerModel(
 
       Vectors.sparse(dictBr.value.size, effectiveCounts)
     }
-    val attrs = vocabulary.map(_ => new NumericAttribute).asInstanceOf[Array[Attribute]]
-    val metadata = new AttributeGroup($(outputCol), attrs).toMetadata()
-    dataset.withColumn($(outputCol), vectorizer(col($(inputCol))), metadata)
+    dataset.withColumn($(outputCol), vectorizer(col($(inputCol))),
+      outputSchema($(outputCol)).metadata)
   }
 
   @Since("1.5.0")
   override def transformSchema(schema: StructType): StructType = {
-    validateAndTransformSchema(schema)
+    var outputSchema = validateAndTransformSchema(schema)
+    if ($(outputCol).nonEmpty) {
+      val attrs: Array[Attribute] = vocabulary.map(_ => new NumericAttribute)
+      val field = new AttributeGroup($(outputCol), attrs).toStructField()
+      outputSchema = SchemaUtils.updateField(outputSchema, field)
 
 Review comment:
   Sounds reasonable, I think we may change this place by only attach a `size`. I will send a follow up.

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