scala - Spark : Average of values instead of sum in reduceByKey using Scala

Question

当调用reduceByKey时，它会将具有相同键的所有值相加。有没有办法计算每个键的平均值？

// I calculate the sum like this and don't know how to calculate the avg
reduceByKey((x,y)=>(x+y)).collect


Array(((Type1,1),4.0), ((Type1,1),9.2), ((Type1,2),8), ((Type1,2),4.5), ((Type1,3),3.5), 
((Type1,3),5.0), ((Type2,1),4.6), ((Type2,1),4), ((Type2,1),10), ((Type2,1),4.3))

Answer 1

一种方法是使用mapValues和reduceByKey，这比aggregateByKey更容易。

.mapValues(value => (value, 1)) // map entry with a count of 1
.reduceByKey {
  case ((sumL, countL), (sumR, countR)) => 
    (sumL + sumR, countL + countR)
}
.mapValues { 
  case (sum , count) => sum / count 
}
.collect

https://www.safaribooksonline.com/library/view/learning-spark/9781449359034/ch04.html