[SPARK-4588] ML Attributes

[mengxr]

This continues the work in #4460 from @srowen . The design doc is published on the JIRA page with some minor changes.

Short description of ML attributes: https://github.com/apache/spark/pull/4925/files?diff=unified#diff-95e7f5060429f189460b44a3f8731a35R24

More details can be found in the design doc.

@srowen Could you help review this PR? There are many lines but most of them are boilerplate code.

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  • sealed abstract class AttributeType(val name: String)
  • sealed abstract class Attribute extends Serializable

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[srowen]

Do you need : String here? also, I may not get the purpose of final here since val is already immutable but would it be simpler to declare the object as final?

[mengxr]

For public fields, we put the types explicitly. You are right about final. An object is already final, we don't need final for its members. I'lll remove them with the next update.

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Test build #28349 has started for PR 4925 at commit 393ffdc.

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Test build #28349 has finished for PR 4925 at commit 393ffdc.

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• This patch adds the following public classes (experimental):
  • sealed abstract class AttributeType(val name: String)
  • sealed abstract class Attribute extends Serializable

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Test build #28357 has started for PR 4925 at commit 617be40.

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Test build #28357 has finished for PR 4925 at commit 617be40.

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• This patch adds the following public classes (experimental):
  • sealed abstract class AttributeType(val name: String)
  • sealed abstract class Attribute extends Serializable

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[jkbradley]

Is there any way to make this doc show up in the Java docs?

[mengxr]

We need package-info.java for Java. Let me include it with the next update.

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Test build #28505 has started for PR 4925 at commit 71d1bd0.

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Test build #28505 has finished for PR 4925 at commit 71d1bd0.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • sealed abstract class AttributeType(val name: String)
  • sealed abstract class Attribute extends Serializable

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[mengxr]

I'm merging this into master, so we can test the APIs in feature transformers. Feel free to propose any changes. Thanks!