### What changes were proposed in this pull request?
The collect_set() aggregate function should produce a set of distinct elements. When the column argument's type is BinayType this is not the case.
Example:
```scala
import org.apache.spark.sql.functions._
import org.apache.spark.sql.expressions.Window
case class R(id: String, value: String, bytes: Array[Byte])
def makeR(id: String, value: String) = R(id, value, value.getBytes)
val df = Seq(makeR("a", "dog"), makeR("a", "cat"), makeR("a", "cat"), makeR("b", "fish")).toDF()
// In the example below "bytesSet" erroneously has duplicates but "stringSet" does not (as expected).
df.agg(collect_set('value) as "stringSet", collect_set('bytes) as "byteSet").show(truncate=false)
// The same problem is displayed when using window functions.
val win = Window.partitionBy('id).rowsBetween(Window.unboundedPreceding, Window.unboundedFollowing)
val result = df.select(
collect_set('value).over(win) as "stringSet",
collect_set('bytes).over(win) as "bytesSet"
)
.select('stringSet, 'bytesSet, size('stringSet) as "stringSetSize", size('bytesSet) as "bytesSetSize")
.show()
```
We use a HashSet buffer to accumulate the results, the problem is that arrays equality in Scala don't behave as expected, arrays ara just plain java arrays and the equality don't compare the content of the arrays
Array(1, 2, 3) == Array(1, 2, 3) => False
The result is that duplicates are not removed in the hashset
The solution proposed is that in the last stage, when we have all the data in the Hashset buffer, we delete duplicates changing the type of the elements and then transform it to the original type.
This transformation is only applied when we have a BinaryType
### Why are the changes needed?
Fix the bug explained
### Does this PR introduce any user-facing change?
Yes. Now `collect_set()` correctly deduplicates array of byte.
### How was this patch tested?
Unit testing
Closes#28351 from planga82/feature/SPARK-31500_COLLECT_SET_bug.
Authored-by: Pablo Langa <soypab@gmail.com>
Signed-off-by: Takeshi Yamamuro <yamamuro@apache.org>
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