如何在 Scala SPARK 中的 groupBy 之后在 agg() 函数中找到分位数

Question

我有一个数据框，我想在其中对 A 列进行分组，然后找到不同的统计数据，例如均值、最小值、最大值、标准偏差和分位数。

我可以使用以下代码找到最小值、最大值和平均值： df.groupBy("A").agg(min("B"), max("B"), mean("B")).show(50, false)

但是我找不到分位数(0.25, 0.5, 0.75)。我尝试了 approxQuantile 和 percentile，但出现以下错误：

错误：未找到：值 approxQuantile

Answer 1

如果类路径中有 Hive，则可以使用许多 UDAF，如 percentile_approx 和 stddev_samp，请参阅 https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF#LanguageManualUDF-Built-inAggregateFunctions(UDAF)

您可以使用 callUDF 调用这些函数：

import ss.implicits._
import org.apache.spark.sql.functions.callUDF

val df = Seq(1.0,2.0,3.0).toDF("x")

df.groupBy()
  .agg(
    callUDF("percentile_approx",$"x",lit(0.5)).as("median"),
    callUDF("stddev_samp",$"x").as("stdev")
  )
.show()

Answer 2

这是我在 Spark 3.1 上测试过的代码

val simpleData = Seq(("James","Sales","NY",90000,34,10000),
    ("Michael","Sales","NY",86000,56,20000),
    ("Robert","Sales","CA",81000,30,23000),
    ("Maria","Finance","CA",90000,24,23000),
    ("Raman","Finance","CA",99000,40,24000),
    ("Scott","Finance","NY",83000,36,19000),
    ("Jen","Finance","NY",79000,53,15000),
    ("Jeff","Marketing","CA",80000,25,18000),
    ("Kumar","Marketing","NY",91000,50,21000)
  )
val df = simpleData.toDF("employee_name","department","state","salary","age","bonus")
df.show()


df.groupBy($"department")
.agg(
 percentile_approx($"salary",lit(0.5), lit(10000))
)
.show(false)

输出

+-------------+----------+-----+------+---+-----+
|employee_name|department|state|salary|age|bonus|
+-------------+----------+-----+------+---+-----+
|        James|     Sales|   NY| 90000| 34|10000|
|      Michael|     Sales|   NY| 86000| 56|20000|
|       Robert|     Sales|   CA| 81000| 30|23000|
|        Maria|   Finance|   CA| 90000| 24|23000|
|        Raman|   Finance|   CA| 99000| 40|24000|
|        Scott|   Finance|   NY| 83000| 36|19000|
|          Jen|   Finance|   NY| 79000| 53|15000|
|         Jeff| Marketing|   CA| 80000| 25|18000|
|        Kumar| Marketing|   NY| 91000| 50|21000|
+-------------+----------+-----+------+---+-----+

+----------+-------------------------------------+
|department|percentile_approx(salary, 0.5, 10000)|
+----------+-------------------------------------+
|Sales     |86000                                |
|Finance   |83000                                |
|Marketing |80000                                |
+----------+-------------------------------------+

如何在 Scala SPARK 中的 groupBy 之后在 agg() 函数中找到分位数

How to find quantiles inside agg() function after groupBy in Scala SPARK

scala

apache-spark

group-by

aggregate

quantile