Scala - Spark In Dataframe 检索具有最大值的行、列名

Question

我有一个数据框:

name     column1  column2  column3  column4
first    2        1        2.1      5.4
test     1.5      0.5      0.9      3.7
choose   7        2.9      9.1      2.5

我想要一个包含包含列的新数据框，列名的行具有最大值:

| name   | max_column |
|--------|------------|
| first  | column4    |
| test   | column4    |
| choose | column3    |

非常感谢您的支持。

Answer 1

可能有更好的方式来编写 UDF。但这可能是可行的解决方案

val spark: SparkSession = SparkSession.builder.master("local").getOrCreate

//implicits for magic functions like .toDf
import spark.implicits._

import org.apache.spark.sql.functions.udf

//We have hard code number of params as UDF don't support variable number of args
val maxval = udf((c1: Double, c2: Double, c3: Double, c4: Double) =>
  if(c1 >= c2 && c1 >= c3 && c1 >= c4)
    "column1"
  else if(c2 >= c1 && c2 >= c3 && c2 >= c4)
    "column2"
  else if(c3 >= c1 && c3 >= c2 && c3 >= c4)
    "column3"
  else
    "column4"
)

//create schema class
case class Record(name: String, 
                    column1: Double, 
                    column2: Double, 
                    column3: Double, 
                    column4: Double)

val df = Seq(
  Record("first", 2.0, 1, 2.1, 5.4),
  Record("test", 1.5, 0.5, 0.9, 3.7),
  Record("choose", 7, 2.9, 9.1, 2.5)
).toDF();

df.withColumn("max_column", maxval($"column1", $"column2", $"column3", $"column4"))
  .select("name", "max_column").show

输出

+------+----------+
|  name|max_column|
+------+----------+
| first|   column4|
|  test|   column4|
|choose|   column3|
+------+----------+