GitHub user liancheng opened a pull request:
https://github.com/apache/spark/pull/11137
[SPARK-13244] [WIP] Prototyping DataFrame to Dataset migration
This PR prototypes the `DataFrame`-to-`Dataset` migration. It demonstrates
main migration strategies but hasn't migrate all `DataFrame` methods.
Compilation/tests may break.
Goals:
1. `Dataset` should have all operations of the original `DataFrame`
1. `DataFrame` is just a special `Dataset[Row]`
1. Source level compatibility whenever possible
Basic strategies used:
1. Migrate all methods in `DataFrame` into `Dataset`
1. Migrate all methods in `GroupedData` into `GroupedDataset[K, V]` and
then remove `GroupedData`
1. Make `DataFrame` extend from `Dataset[Row]`
Overrides untyped `Dataset` operations in `DataFrame` and make them
return `DataFrame` instead of `Dataset[Row]`
For all untyped methods (typically those take `String`s and `Column`s as
arguments), make them return `Row`, `Dataset[Row]`, or `GroupedDataset[Row, T]`.
Problems encountered:
1. `DataFrame` RDD operations conflict with `Dataset` functional operations
E.g.: `df.map` returns an RDD while `df.map` returns a `Dataset`.
Possible solutions:
- Remove `DataFrame` RDD operations since they can be easily mapped
to methods of `df.rdd.
Cons: breaks source level compatibility
- Rename those `Dataset` methods
Cons: may result inconsistent naming
Personally I prefer the former option.
2. `Dataset` methods returning arrays can't be overriden in `DataFrame`
E.g.: `Dataset.randomSplit` returns `Array[Dataset[T]]`. We can't have
an override version for `DataFrame` and make it return `Array[DataFrame]`.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/liancheng/spark df-to-ds
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/11137.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #11137
----
commit dbc1a00635b737d3ca86ce08e3072b903620119a
Author: Cheng Lian <[email protected]>
Date: 2016-02-09T17:22:46Z
WIP: prototyping DataFrame to Dataset migration
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