如何在Scala Spark中使用window lag来查找更改

import org.apache.spark.sql.functions._
import org.apache.spark.sql.expressions.Window

val spark = SparkSession.builder()
  .appName("Window Lag Example")
  .getOrCreate()

val data = Seq(
  ("A", 10),
  ("A", 20),
  ("B", 15),
  ("B", 25),
  ("B", 30)
).toDF("key", "value")

val windowSpec = Window.partitionBy("key").orderBy("value")

val result = data.withColumn("prev_value", lag("value", 1).over(windowSpec))

result.show()

+---+-----+----------+
|key|value|prev_value|
+---+-----+----------+
|  A|   10|      null|
|  A|   20|        10|
|  B|   15|      null|
|  B|   25|        15|
|  B|   30|        25|
+---+-----+----------+