Cumulative product in Spark - scala

Question

I try to implement a cumulative product in Spark Scala, but I really don't know how to it. I have the following dataframe:
Input data:
+--+--+--------+----+
|A |B | date | val|
+--+--+--------+----+
|rr|gg|20171103| 2 |
|hh|jj|20171103| 3 |
|rr|gg|20171104| 4 |
|hh|jj|20171104| 5 |
|rr|gg|20171105| 6 |
|hh|jj|20171105| 7 |
+-------+------+----+
And I would like to have the following output:
Output data:
+--+--+--------+-----+
|A |B | date | val |
+--+--+--------+-----+
|rr|gg|20171105| 48 | // 2 * 4 * 6
|hh|jj|20171105| 105 | // 3 * 5 * 7
+-------+------+-----+

Answer 1

As long as the number are strictly positive (0 can be handled as well, if present, using coalesce) as in your example, the simplest solution is to compute the sum of logarithms and take the exponential:
import org.apache.spark.sql.functions.{exp, log, max, sum}
val df = Seq(
("rr", "gg", "20171103", 2), ("hh", "jj", "20171103", 3),
("rr", "gg", "20171104", 4), ("hh", "jj", "20171104", 5),
("rr", "gg", "20171105", 6), ("hh", "jj", "20171105", 7)
).toDF("A", "B", "date", "val")
val result = df
.groupBy("A", "B")
.agg(
max($"date").as("date"),
exp(sum(log($"val"))).as("val"))
Since this uses FP arithmetic the result won't be exact:
result.show
+---+---+--------+------------------+
| A| B| date| val|
+---+---+--------+------------------+
| hh| jj|20171105|104.99999999999997|
| rr| gg|20171105|47.999999999999986|
+---+---+--------+------------------+
but after rounding should good enough for majority of applications.
result.withColumn("val", round($"val")).show
+---+---+--------+-----+
| A| B| date| val|
+---+---+--------+-----+
| hh| jj|20171105|105.0|
| rr| gg|20171105| 48.0|
+---+---+--------+-----+
If that's not enough you can define an UserDefinedAggregateFunction or Aggregator (How to define and use a User-Defined Aggregate Function in Spark SQL?) or use functional API with reduceGroups:
import scala.math.Ordering
case class Record(A: String, B: String, date: String, value: Long)
df.withColumnRenamed("val", "value").as[Record]
.groupByKey(x => (x.A, x.B))
.reduceGroups((x, y) => x.copy(
date = Ordering[String].max(x.date, y.date),
value = x.value * y.value))
.toDF("key", "value")
.select($"value.*")
.show
+---+---+--------+-----+
| A| B| date|value|
+---+---+--------+-----+
| hh| jj|20171105| 105|
| rr| gg|20171105| 48|
+---+---+--------+-----+

Answer 2

You can solve this using either collect_list+UDF or an UDAF. UDAF may be more efficient, but harder to implement due to the local aggregation.
If you have a dataframe like this :
+---+---+
|key|val|
+---+---+
| a| 1|
| a| 2|
| a| 3|
| b| 4|
| b| 5|
+---+---+
You can invoke an UDF :
val prod = udf((vals:Seq[Int]) => vals.reduce(_ * _))
df
.groupBy($"key")
.agg(prod(collect_list($"val")).as("val"))
.show()
+---+---+
|key|val|
+---+---+
| b| 20|
| a| 6|
+---+---+

Answer 3

Since Spark 2.4, you could also compute this using the higher order function aggregate:
import org.apache.spark.sql.functions.{expr, max}
val df = Seq(
("rr", "gg", "20171103", 2),
("hh", "jj", "20171103", 3),
("rr", "gg", "20171104", 4),
("hh", "jj", "20171104", 5),
("rr", "gg", "20171105", 6),
("hh", "jj", "20171105", 7)
).toDF("A", "B", "date", "val")
val result = df
.groupBy("A", "B")
.agg(
max($"date").as("date"),
expr("""
aggregate(
collect_list(val),
cast(1 as bigint),
(acc, x) -> acc * x)""").alias("val")
)

Answer 4

Spark 3.2+
product(e: Column): Column
Aggregate function: returns the product of all numerical elements in a group.
Scala
import spark.implicits._
var df = Seq(
("rr", "gg", 20171103, 2),
("hh", "jj", 20171103, 3),
("rr", "gg", 20171104, 4),
("hh", "jj", 20171104, 5),
("rr", "gg", 20171105, 6),
("hh", "jj", 20171105, 7)
).toDF("A", "B", "date", "val")
df = df.groupBy("A", "B").agg(max($"date").as("date"), product($"val").as("val"))
df.show(false)
// +---+---+--------+-----+
// |A |B |date |val |
// +---+---+--------+-----+
// |hh |jj |20171105|105.0|
// |rr |gg |20171105|48.0 |
// +---+---+--------+-----+
PySpark
from pyspark.sql import SparkSession, functions as F
spark = SparkSession.builder.getOrCreate()
data = [('rr', 'gg', 20171103, 2),
('hh', 'jj', 20171103, 3),
('rr', 'gg', 20171104, 4),
('hh', 'jj', 20171104, 5),
('rr', 'gg', 20171105, 6),
('hh', 'jj', 20171105, 7)]
df = spark.createDataFrame(data, ['A', 'B', 'date', 'val'])
df = df.groupBy('A', 'B').agg(F.max('date').alias('date'), F.product('val').alias('val'))
df.show()
#+---+---+--------+-----+
#| A| B| date| val|
#+---+---+--------+-----+
#| hh| jj|20171105|105.0|
#| rr| gg|20171105| 48.0|
#+---+---+--------+-----+