我试图在sparkDataframe中执行分层采样，但是sampleby函数的行为（奇怪地）类似于sample。
spark版本3.0.1

import spark.implicits._

val data = Seq( ("Java", 20000), ("Java", 10000), ("Java", 3000),  ("Java", 17000),
                ("Python", 100000), ("Python", 20000),
                ("Scala", 3000), ("Scala", 4000), ("Scala", 1000), ("Scala", 43000), ("Scala", 2000), ("Scala", 9000)).toDF("Language", "Price")
val sample_size = 0.5
val seed = 762387
val stratify = "Language"

val subsample = data.sample(withReplacement=false, fraction=sample_size, seed=seed)

subsample.show()

val fractions = data.select(stratify).distinct().as[String].collect().map((_, sample_size)).toMap
println(fractions.mkString("\n")
val stratified_subsample = data.stat.sampleBy(stratify, fractions=fractions, seed=seed)

stratified_subsample.show()

输出：

+--------+------+
|Language| Price|
+--------+------+
|    Java|  3000|
|  Python|100000|
|  Python| 20000|
|   Scala|  3000|
|   Scala| 43000|
|   Scala|  2000|
|   Scala|  9000|
+--------+------+

Scala -> 0.5
Python -> 0.5
Java -> 0.5

+--------+------+
|Language| Price|
+--------+------+
|    Java|  3000|
|  Python|100000|
|  Python| 20000|
|   Scala|  3000|
|   Scala| 43000|
|   Scala|  2000|
|   Scala|  9000|
+--------+------+

另一个种子的输出（6354345）：

+--------+------+
|Language| Price|
+--------+------+
|    Java| 10000|
|    Java| 17000|
|  Python|100000|
|   Scala|  3000|
|   Scala|  4000|
|   Scala|  1000|
|   Scala| 43000|
|   Scala|  2000|
|   Scala|  9000|
+--------+------+

Scala -> 0.5
Python -> 0.5
Java -> 0.5

+--------+------+
|Language| Price|
+--------+------+
|    Java| 10000|
|    Java| 17000|
|  Python|100000|
|   Scala|  3000|
|   Scala|  4000|
|   Scala|  1000|
|   Scala| 43000|
|   Scala|  2000|
|   Scala|  9000|
+--------+------+

我尝试了不同的Dataframe，不同的种子，两个Dataframe总是相等的。我总是有同样的行为，样本根本没有分层。我知道sampleby并不精确，但有同样的行为似乎不好。我的片段有问题吗？