在spark中，遍历每一列并找到最大长度

import org.apache.spark.sql.functions._
import org.apache.spark.sql.types._

val data = Seq(
  ("John", "Doe", 25),
  ("Jane", "Smith", 30),
  ("Bob", "Johnson", 35)
)
val schema = StructType(Seq(
  StructField("first_name", StringType, nullable = false),
  StructField("last_name", StringType, nullable = false),
  StructField("age", IntegerType, nullable = false)
))
val df = spark.createDataFrame(spark.sparkContext.parallelize(data), schema)

def getMaxColumnLength(df: DataFrame): Map[String, Int] = {
  val columnLengths = df.schema.fields.map { field =>
    val columnName = field.name
    val columnType = field.dataType
    val maxLength = df.select(length(col(columnName))).as[Int].collect.max
    (columnName, maxLength)
  }
  columnLengths.toMap
}

val maxColumnLengths = getMaxColumnLength(df)
maxColumnLengths.foreach { case (columnName, maxLength) =>
  println(s"Max length of column '$columnName': $maxLength")
}