Spark数据帧中两行之间的差异 [英] Difference between two rows in Spark dataframe

问题描述

我在 Spark 中通过 groupby column1 和 date 创建了一个数据框并计算了数量.

I created a dataframe in Spark, by groupby column1 and date and calculated the amount.

val table = df1.groupBy($"column1",$"date").sum("amount")

Column1 |Date   |Amount
A   |1-jul  |1000
A   |1-june |2000
A   |1-May  |2000
A   |1-dec  |3000
A   |1-Nov  |2000
B   |1-jul  |100
B   |1-june |300    
B   |1-May  |400
B   |1-dec  |300

现在，我想添加新列，表中任意两个日期的数量之间存在差异.

Now, I want to add new column, with difference between amount of any two dates from the table.

推荐答案

如果计算固定为计算前几个月之间的差异，您可以使用Window函数，或者前两个月之间的计算 ...等.为此，您可以使用 lag 和 lead 功能和 Window.

You can use Window function if the calculation is fixed as calculating difference between previous months, or calculating between previous two months ... etc. For that you can use lag and lead function with Window.

但为此您需要更改日期列，如下所示，以便可以订购.

But for that you need to change the date column as below so that it can be ordered.

+-------+------+--------------+------+
|Column1|Date  |Date_Converted|Amount|
+-------+------+--------------+------+
|A      |1-jul |2017-07-01    |1000  |
|A      |1-june|2017-06-01    |2000  |
|A      |1-May |2017-05-01    |2000  |
|A      |1-dec |2017-12-01    |3000  |
|A      |1-Nov |2017-11-01    |2000  |
|B      |1-jul |2017-07-01    |100   |
|B      |1-june|2017-06-01    |300   |
|B      |1-May |2017-05-01    |400   |
|B      |1-dec |2017-12-01    |300   |
+-------+------+--------------+------+

您可以通过执行

import org.apache.spark.sql.expressions._
val windowSpec = Window.partitionBy("Column1").orderBy("Date_Converted")
import org.apache.spark.sql.functions._
df.withColumn("diff_Amt_With_Prev_Month", $"Amount" - when((lag("Amount", 1).over(windowSpec)).isNull, 0).otherwise(lag("Amount", 1).over(windowSpec)))
   .show(false)

你应该有

+-------+------+--------------+------+------------------------+
|Column1|Date  |Date_Converted|Amount|diff_Amt_With_Prev_Month|
+-------+------+--------------+------+------------------------+
|B      |1-May |2017-05-01    |400   |400.0                   |
|B      |1-june|2017-06-01    |300   |-100.0                  |
|B      |1-jul |2017-07-01    |100   |-200.0                  |
|B      |1-dec |2017-12-01    |300   |200.0                   |
|A      |1-May |2017-05-01    |2000  |2000.0                  |
|A      |1-june|2017-06-01    |2000  |0.0                     |
|A      |1-jul |2017-07-01    |1000  |-1000.0                 |
|A      |1-Nov |2017-11-01    |2000  |1000.0                  |
|A      |1-dec |2017-12-01    |3000  |1000.0                  |
+-------+------+--------------+------+------------------------+

您可以将前两个月的滞后头寸增加为

You can increase the lagging position for previous two months as

df.withColumn("diff_Amt_With_Prev_two_Month", $"Amount" - when((lag("Amount", 2).over(windowSpec)).isNull, 0).otherwise(lag("Amount", 2).over(windowSpec)))
  .show(false)

这会给你

+-------+------+--------------+------+----------------------------+
|Column1|Date  |Date_Converted|Amount|diff_Amt_With_Prev_two_Month|
+-------+------+--------------+------+----------------------------+
|B      |1-May |2017-05-01    |400   |400.0                       |
|B      |1-june|2017-06-01    |300   |300.0                       |
|B      |1-jul |2017-07-01    |100   |-300.0                      |
|B      |1-dec |2017-12-01    |300   |0.0                         |
|A      |1-May |2017-05-01    |2000  |2000.0                      |
|A      |1-june|2017-06-01    |2000  |2000.0                      |
|A      |1-jul |2017-07-01    |1000  |-1000.0                     |
|A      |1-Nov |2017-11-01    |2000  |0.0                         |
|A      |1-dec |2017-12-01    |3000  |2000.0                      |
+-------+------+--------------+------+----------------------------+

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