spark sql窗口函数滞后

Question

我在Spark SQL,Scala中查看Spark DataFrame的窗口滑动功能.

我有一个数据框,列Col1,Col1,Col1,日期.

Col1    Col2    Col3    date     volume new_col
                        201601  100.5   
                        201602  120.6   100.5
                        201603  450.2   120.6
                        201604  200.7   450.2
                        201605  121.4   200.7`

现在我想添加一个名为(new_col)的新列,其中一行向下滑动,如上所示.

我试过下面的选项来使用窗口功能.

val windSldBrdrxNrx_df = df.withColumn("Prev_brand_rx", lag("Prev_brand_rx",1))

任何人都可以帮助我如何做到这一点.

Answer 1

你正在做正确,你错过了所有的over(window expression)上lag

val df = sc.parallelize(Seq((201601, 100.5),
  (201602, 120.6),
  (201603, 450.2),
  (201604, 200.7),
  (201605, 121.4))).toDF("date", "volume")

val w = org.apache.spark.sql.expressions.Window.orderBy("date")  

import org.apache.spark.sql.functions.lag

val leadDf = df.withColumn("new_col", lag("volume", 1, 0).over(w))

leadDf.show()

+------+------+-------+
|  date|volume|new_col|
+------+------+-------+
|201601| 100.5|    0.0|
|201602| 120.6|  100.5|
|201603| 450.2|  120.6|
|201604| 200.7|  450.2|
|201605| 121.4|  200.7|
+------+------+-------+

此代码在Spark shell 2.0.2上运行