诀窍是应用窗口函数。解决方案如下:
scala> val df = Seq(
| | ("M1",100,200,1),
| | ("M1",100,175,2),
| | ("M1",101,150,3),
| | ("M1",100,125,4),
| | ("M1",100,90,5),
| | ("M1",100,85,6),
| | ("M2",200,1001,1),
| | ("M2",200,500,2),
| | ("M2",200,456,3),
| | ("M2",200,345,4),
| | ("M2",200,231,5),
| | ("M2",201,123,6)
| | ).toDF("M","M_Max","Sales","Rank")
df: org.apache.spark.sql.DataFrame = [M: string, M_Max: int ... 2 more fields]
scala> import org.apache.spark.sql.expressions.Window
import org.apache.spark.sql.expressions.Window
scala> val w = Window.partitionBy("M")
w: org.apache.spark.sql.expressions.WindowSpec = org.apache.spark.sql.expressions.WindowSpec@49b4e11c
scala> df.withColumn("new", max("M_Max") over (w)).groupBy("M", "new").pivot("Rank").agg(first("Sales")).withColumnRenamed("new", "M_Max").show
+---+-----+----+---+---+---+---+---+
| M|M_Max| 1| 2| 3| 4| 5| 6|
+---+-----+----+---+---+---+---+---+
| M1| 101| 200|175|150|125| 90| 85|
| M2| 201|1001|500|456|345|231|123|
+---+-----+----+---+---+---+---+---+
scala> df.show
+---+-----+-----+----+
| M|M_Max|Sales|Rank|
+---+-----+-----+----+
| M1| 100| 200| 1|
| M1| 100| 175| 2|
| M1| 101| 150| 3|
| M1| 100| 125| 4|
| M1| 100| 90| 5|
| M1| 100| 85| 6|
| M2| 200| 1001| 1|
| M2| 200| 500| 2|
| M2| 200| 456| 3|
| M2| 200| 345| 4|
| M2| 200| 231| 5|
| M2| 201| 123| 6|
+---+-----+-----+----+
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