Calculating Cumulative sum in PySpark using Window Functions

问题

I have the following sample DataFrame:

rdd = sc.parallelize([(1,20), (2,30), (3,30)])
df2 = spark.createDataFrame(rdd, ["id", "duration"])
df2.show()

+---+--------+
| id|duration|
+---+--------+
|  1|      20|
|  2|      30|
|  3|      30|
+---+--------+

I want to sort this DataFrame in desc order of duration and add a new column which has the cumulative sum of the duration. So I did the following:

windowSpec = Window.orderBy(df2['duration'].desc())

df_cum_sum = df2.withColumn("duration_cum_sum", sum('duration').over(windowSpec))

df_cum_sum.show()

+---+--------+----------------+
| id|duration|duration_cum_sum|
+---+--------+----------------+
|  2|      30|              60|
|  3|      30|              60|
|  1|      20|              80|
+---+--------+----------------+

My desired output is:

+---+--------+----------------+
| id|duration|duration_cum_sum|
+---+--------+----------------+
|  2|      30|              30| 
|  3|      30|              60| 
|  1|      20|              80|
+---+--------+----------------+

How do I get this?

Here is the breakdown:

+--------+----------------+
|duration|duration_cum_sum|
+--------+----------------+
|      30|              30| #First value
|      30|              60| #Current duration + previous cum sum value
|      20|              80| #Current duration + previous cum sum value     
+--------+----------------+

回答1:

You can introduce the row_number to break the ties; If written in sql:

df2.selectExpr(
    "id", "duration", 
    "sum(duration) over (order by row_number() over (order by duration desc)) as duration_cum_sum"
 ).show()

+---+--------+----------------+
| id|duration|duration_cum_sum|
+---+--------+----------------+
|  2|      30|              30|
|  3|      30|              60|
|  1|      20|              80|
+---+--------+----------------+

回答2:

Here you can check this

df2.withColumn('cumu', F.sum('duration').over(Window.orderBy(F.col('duration').desc()).rowsBetween(Window.unboundedPreceding, 0)
)).show()

来源：https://stackoverflow.com/questions/46979685/calculating-cumulative-sum-in-pyspark-using-window-functions

标签

python

pyspark