重命名Spark DataFrame中的嵌套结构列

Question

我正在尝试在Scala中更改DataFrame列的名称。我可以轻松更改直接字段的列名，但在转换数组结构列时遇到困难。

以下是我的DataFrame模式。

|-- _VkjLmnVop: string (nullable = true)
|-- _KaTasLop: string (nullable = true)
|-- AbcDef: struct (nullable = true)
 |    |-- UvwXyz: struct (nullable = true)
 |    |    |-- _MnoPqrstUv: string (nullable = true)
 |    |    |-- _ManDevyIxyz: string (nullable = true)

但我需要如下所示的架构

|-- vkj_lmn_vop: string (nullable = true)
|-- ka_tas_lop: string (nullable = true)
|-- abc_def: struct (nullable = true)
 |    |-- uvw_xyz: struct (nullable = true)
 |    |    |-- mno_pqrst_uv: string (nullable = true)
 |    |    |-- man_devy_ixyz: string (nullable = true)

对于非结构列，我在下面更改列名称

def aliasAllColumns(df: DataFrame): DataFrame = {
  df.select(df.columns.map { c =>
    df.col(c)
      .as(
        c.replaceAll("_", "")
          .replaceAll("([A-Z])", "_$1")
          .toLowerCase
          .replaceFirst("_", ""))
  }: _*)
}
aliasAllColumns(file_data_df).show(1)

如何动态更改Struct列名？

Answer 1

您可以创建一个递归方法来遍历DataFrame模式以重命名列：

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

def renameAllCols(schema: StructType, rename: String => String): StructType = {
  def recurRename(schema: StructType): Seq[StructField] = schema.fields.map{
      case StructField(name, dtype: StructType, nullable, meta) =>
        StructField(rename(name), StructType(recurRename(dtype)), nullable, meta)
      case StructField(name, dtype, nullable, meta) =>
        StructField(rename(name), dtype, nullable, meta)
    }
  StructType(recurRename(schema))
}

使用以下示例对其进行测试：

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

val renameFcn = (s: String) =>
  s.replace("_", "").replaceAll("([A-Z])", "_$1").toLowerCase.dropWhile(_ == '_')

case class C(A_Bc: Int, D_Ef: Int)

val df = Seq(
  (10, "a", C(1, 2)),
  (20, "b", C(3, 4))
).toDF("_VkjLmnVop", "_KaTasLop", "AbcDef")

val newDF = spark.createDataFrame(df.rdd, renameAllCols(df.schema, renameFcn))

newDF.printSchema
// root
//  |-- vkj_lmn_vop: integer (nullable = false)
//  |-- ka_tas_lop: string (nullable = true)
//  |-- abc_def: struct (nullable = true)
//  |    |-- a_bc: integer (nullable = false)
//  |    |-- d_ef: integer (nullable = false)