如何按组使用roximateQuantile? [英] How to use approxQuantile by group?
问题描述
Spark具有SQL函数percentile_approx()
,它的Scala副本是df.stat.approxQuantile()
.
Spark has SQL function percentile_approx()
, and its Scala counterpart is df.stat.approxQuantile()
.
但是,Scala副本不能用于分组数据集,例如df.groupby("foo").stat.approxQuantile()
,如下所示: https://stackoverflow.com/a/51933027 .
However, the Scala counterpart cannot be used on grouped datasets, something like df.groupby("foo").stat.approxQuantile()
, as answered here: https://stackoverflow.com/a/51933027.
但是可以用SQL语法进行分组和百分位.所以我想知道,也许可以从SQL percentile_approx
函数定义一个UDF并将其用于我的分组数据集中吗?
But it's possible to do both grouping and percentiles in SQL syntax. So I'm wondering, maybe I can define an UDF from SQL percentile_approx
function and use it on my grouped dataset?
推荐答案
火花> = 3.1
Spark 3.1中已添加了相应的SQL函数-请参见 SPARK-30569 .
Corresponding SQL functions have been added in Spark 3.1 - see SPARK-30569.
火花< 3.1
虽然您不能在UDF中使用approxQuantile
,并且没有percentile_approx
的Scala包装器,但自己实现一个并不难:
While you cannot use approxQuantile
in an UDF, and you there is no Scala wrapper for percentile_approx
it is not hard to implement one yourself:
import org.apache.spark.sql.functions._
import org.apache.spark.sql.Column
import org.apache.spark.sql.catalyst.expressions.aggregate.ApproximatePercentile
object PercentileApprox {
def percentile_approx(col: Column, percentage: Column, accuracy: Column): Column = {
val expr = new ApproximatePercentile(
col.expr, percentage.expr, accuracy.expr
).toAggregateExpression
new Column(expr)
}
def percentile_approx(col: Column, percentage: Column): Column = percentile_approx(
col, percentage, lit(ApproximatePercentile.DEFAULT_PERCENTILE_ACCURACY)
)
}
示例用法:
import PercentileApprox._
val df = (Seq.fill(100)("a") ++ Seq.fill(100)("b")).toDF("group").withColumn(
"value", when($"group" === "a", randn(1) + 10).otherwise(randn(3))
)
df.groupBy($"group").agg(percentile_approx($"value", lit(0.5))).show
+-----+------------------------------------+
|group|percentile_approx(value, 0.5, 10000)|
+-----+------------------------------------+
| b| -0.06336346702250675|
| a| 9.818985618591595|
+-----+------------------------------------+
df.groupBy($"group").agg(
percentile_approx($"value", typedLit(Seq(0.1, 0.25, 0.75, 0.9)))
).show(false)
+-----+----------------------------------------------------------------------------------+
|group|percentile_approx(value, [0.1,0.25,0.75,0.9], 10000) |
+-----+----------------------------------------------------------------------------------+
|b |[-1.2098351202406483, -0.6640768986666159, 0.6778253126144265, 1.3255676906697658]|
|a |[8.902067202468098, 9.290417382259626, 10.41767257153993, 11.067087075488068] |
+-----+----------------------------------------------------------------------------------+
一旦它在JVM类路径上,您还可以使用类似于内置函数的逻辑来添加PySpark包装器.
Once this is on the JVM classpath you can also add PySpark wrapper, using logic similar to built-in functions.
这篇关于如何按组使用roximateQuantile?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!