问题
In Spark 1.6.0 / Scala, is there an opportunity to get collect_list("colC") or collect_set("colC").over(Window.partitionBy("colA").orderBy("colB")?
回答1:
Given that you have dataframe as
+----+----+----+
|colA|colB|colC|
+----+----+----+
|1 |1 |23 |
|1 |2 |63 |
|1 |3 |31 |
|2 |1 |32 |
|2 |2 |56 |
+----+----+----+
You can Window functions by doing the following
import org.apache.spark.sql.functions._
import org.apache.spark.sql.expressions._
df.withColumn("colD", collect_list("colC").over(Window.partitionBy("colA").orderBy("colB"))).show(false)
Result:
+----+----+----+------------+
|colA|colB|colC|colD |
+----+----+----+------------+
|1 |1 |23 |[23] |
|1 |2 |63 |[23, 63] |
|1 |3 |31 |[23, 63, 31]|
|2 |1 |32 |[32] |
|2 |2 |56 |[32, 56] |
+----+----+----+------------+
Similar is the result for collect_set as well. But the order of elements in the final set will not be in order as with collect_list
df.withColumn("colD", collect_set("colC").over(Window.partitionBy("colA").orderBy("colB"))).show(false)
+----+----+----+------------+
|colA|colB|colC|colD |
+----+----+----+------------+
|1 |1 |23 |[23] |
|1 |2 |63 |[63, 23] |
|1 |3 |31 |[63, 31, 23]|
|2 |1 |32 |[32] |
|2 |2 |56 |[56, 32] |
+----+----+----+------------+
If you remove orderBy as below
df.withColumn("colD", collect_list("colC").over(Window.partitionBy("colA"))).show(false)
result would be
+----+----+----+------------+
|colA|colB|colC|colD |
+----+----+----+------------+
|1 |1 |23 |[23, 63, 31]|
|1 |2 |63 |[23, 63, 31]|
|1 |3 |31 |[23, 63, 31]|
|2 |1 |32 |[32, 56] |
|2 |2 |56 |[32, 56] |
+----+----+----+------------+
I hope the answer is helpful
来源：https://stackoverflow.com/questions/45131481/how-to-use-collect-set-and-collect-list-functions-in-windowed-aggregation-in-spa