[jira] [Created] (SPARK-14585) Provide accessor methods for Pipeline stages

["Joseph K. Bradley (JIRA)" <ji...@apache.org>]

Joseph K. Bradley created SPARK-14585:
-----------------------------------------

             Summary: Provide accessor methods for Pipeline stages
                 Key: SPARK-14585
                 URL: https://issues.apache.org/jira/browse/SPARK-14585
             Project: Spark
          Issue Type: New Feature
          Components: ML
            Reporter: Joseph K. Bradley


It is currently hard to access particular stages in a Pipeline or PipelineModel.  Some accessor methods would help.

Scala:
{code}
class Pipeline {
  /** Returns stage at index i in Pipeline */
  def getStage[T <: PipelineStage](i: Int): T

  /** Returns all stages of this type */
  def getStagesOfType[T <: PipelineStage]: Array[T]
}

class PipelineModel {
  /** Returns stage at index i in PipelineModel */
  def getStage[T <: Transformer](i: Int): T

  /**
   * Returns stage given its parent or generating instance in PipelineModel.
   * E.g., if this PipelineModel was created from a Pipeline containing a stage 
   * {{myStage}}, then passing {{myStage}} to this method will return the
   * corresponding stage in this PipelineModel.
   */
  def getStage[T <: Transformer][implicit E <: PipelineStage](stage: E): T

  /** Returns all stages of this type */
  def getStagesOfType[T <: Transformer]: Array[T]
}
{code}

These methods should not be recursive for now.  I.e., if a Pipeline A contains another Pipeline B, then calling {{getStage}} on the outer Pipeline A should not search for the stage within Pipeline B.




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