spark dataframe 保留小數位數

import org.spache.spark.sql.functions._
import spark.implicits._

val df = sc.parallelize(Array(1.2,1.233453,2.45323445,3.22))

val df1 = df.toDF()

df1.show()

val df2 = df1.select(bround($"value",scale=4).alias("RankPoint"))

val df3 = df1.selectExpr("cast(value as decimal(18,4)) as RankPoint")