[GitHub] [spark] zhengruifeng commented on issue #27003: [SPARK-30347][ML] LibSVMDataSource attach AttributeGroup

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zhengruifeng commented on issue #27003: [SPARK-30347][ML] LibSVMDataSource attach AttributeGroup
URL: https://github.com/apache/spark/pull/27003#issuecomment-568722282
 
 
   After this PR, `LibSVMDataSource` will attach `AttributeGroup` for ML impls, while keep current metata.
   ```scala
   scala> import org.apache.spark.ml.attribute._
   import org.apache.spark.ml.attribute._
   
   scala> val data = spark.read.format("libsvm").load("/data0/Dev/Opensource/spark/data/mllib/sample_multiclass_classification_data.txt")
   19/12/24 18:47:35 WARN LibSVMFileFormat: 'numFeatures' option not specified, determining the number of features by going though the input. If you know the number in advance, please specify it via 'numFeatures' option to avoid the extra scan.
   data: org.apache.spark.sql.DataFrame = [label: double, features: vector]
   
   scala> data.schema("features").metadata
   res0: org.apache.spark.sql.types.Metadata = {"ml_attr":{"num_attrs":4},"numFeatures":4}
   
   scala> AttributeGroup.fromStructField(data.schema("features")).size
   res1: Int = 4
   ```

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