fqaiser94 opened a new pull request #27066: [SPARK-22231][SQL] Add withField method to Column class URL: https://github.com/apache/spark/pull/27066 ### What changes were proposed in this pull request? <!-- Please clarify what changes you are proposing. The purpose of this section is to outline the changes and how this PR fixes the issue. If possible, please consider writing useful notes for better and faster reviews in your PR. See the examples below. 1. If you refactor some codes with changing classes, showing the class hierarchy will help reviewers. 2. If you fix some SQL features, you can provide some references of other DBMSes. 3. If there is design documentation, please add the link. 4. If there is a discussion in the mailing list, please add the link. --> Added a new `withField` method to the `Column` class. This method should allow users to add or replace a `StructField` in a `StructType` column (much like how the `withColumn` method on the `Dataset` class operates). ### Why are the changes needed? <!-- Please clarify why the changes are needed. For instance, 1. If you propose a new API, clarify the use case for a new API. 2. If you fix a bug, you can clarify why it is a bug. --> Often Spark users have to work with deeply nested data e.g. to fix a data quality issue with an existing `StructField`. To do this with the existing Spark APIs, users have to rebuild the entire struct column. For example, let's say you have the following data which has a quality issue (`5` is missing): ``` import org.apache.spark.sql._ import org.apache.spark.sql.functions._ import org.apache.spark.sql.types._ val data = spark.createDataFrame(sc.parallelize( Seq(Row(Row(Row(1, 2, 3), Row(Row(4, null, 6), Row(7, 8, 9), Row(10, 11, 12)), Row(13, 14, 15))))), StructType(Seq( StructField("a", StructType(Seq( StructField("a", StructType(Seq( StructField("a", IntegerType), StructField("b", IntegerType), StructField("c", IntegerType)))), StructField("b", StructType(Seq( StructField("a", StructType(Seq( StructField("a", IntegerType), StructField("b", IntegerType), StructField("c", IntegerType)))), StructField("b", StructType(Seq( StructField("a", IntegerType), StructField("b", IntegerType), StructField("c", IntegerType)))), StructField("c", StructType(Seq( StructField("a", IntegerType), StructField("b", IntegerType), StructField("c", IntegerType)))) ))), StructField("c", StructType(Seq( StructField("a", IntegerType), StructField("b", IntegerType), StructField("c", IntegerType)))) )))))).cache data.show(false) +---------------------------------+ |a | +---------------------------------+ |[[1, 2, 3], [[4,, 6], [7, 8, 9]]]| +---------------------------------+ ``` Currently, to replace the missing value users would have to do something like this: ``` val result = data.withColumn("a", struct( $"a.a", struct( struct( $"a.b.a.a", lit(5).as("b"), $"a.b.a.c" ).as("a"), $"a.b.b", $"a.b.c" ).as("b"), $"a.c" )) result.show(false) +---------------------------------------------------------------+ |a | +---------------------------------------------------------------+ |[[1, 2, 3], [[4, 5, 6], [7, 8, 9], [10, 11, 12]], [13, 14, 15]]| +---------------------------------------------------------------+ ``` As you can see above, with the existing methods users must call the `struct` function and list all fields, including fields they don't want to manipulate. This is not ideal as: >this leads to complex, fragile code that cannot survive schema evolution. [SPARK-16483](https://issues.apache.org/jira/browse/SPARK-16483) In contrast, with the methods added in this PR, a user could simply do something like this: ``` val result = data.withColumn("a", 'a.withField( "b", $"a.b".withField( "a", $"a.b.a".withField( "b", lit(5))))) result.show(false) +-----------------------------------+ |a | +-----------------------------------+ |[[1, 2, 3], [[4, 5, 6], [7, 8, 9]]]| +-----------------------------------+ ``` This is shorter, and more importantly can survive schema evolution. You could even further condense this code with a simple utility function: ``` ``` This is the first of maybe a few methods that could be added to the `Column` class to make it easier to manipulate nested data. Other methods under discussion in [SPARK-22231](https://issues.apache.org/jira/browse/SPARK-22231) include `drop` and `renameField`. However, these should be added in a separate PR. ### Does this PR introduce any user-facing change? <!-- If yes, please clarify the previous behavior and the change this PR proposes - provide the console output, description and/or an example to show the behavior difference if possible. If no, write 'No'. --> No. ### How was this patch tested? <!-- If tests were added, say they were added here. Please make sure to add some test cases that check the changes thoroughly including negative and positive cases if possible. If it was tested in a way different from regular unit tests, please clarify how you tested step by step, ideally copy and paste-able, so that other reviewers can test and check, and descendants can verify in the future. If tests were not added, please describe why they were not added and/or why it was difficult to add. --> New unit tests were added. Jenkins must pass them. ### Related JIRAs: - https://issues.apache.org/jira/browse/SPARK-22231 - https://issues.apache.org/jira/browse/SPARK-16483
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