scala – 从Spark DataFrame中删除一个嵌套列

发布时间：2020-12-16 19:07:16 所属栏目：安全来源：网络整理

我有一个DataFrame与模式

root
 |-- label: string (nullable = true)
 |-- features: struct (nullable = true)
 |    |-- feat1: string (nullable = true)
 |    |-- feat2: string (nullable = true)
 |    |-- feat3: string (nullable = true)

虽然,我可以使用过滤数据框

val data = rawData
     .filter( !(rawData("features.feat1") <=> "100") )

我无法删除列

val data = rawData
       .drop("features.feat1")

这是我在这里做错了吗？我也尝试(不成功)做drop(rawData(“features.feat1”)),尽管这样做没有什么意义.

提前致谢,

尼基尔

解决方法

这只是一个编程练习,但你可以尝试这样的：

import org.apache.spark.sql.{DataFrame,Column}
import org.apache.spark.sql.types.{StructType,StructField}
import org.apache.spark.sql.{functions => f}
import scala.util.Try

case class DFWithDropFrom(df: DataFrame) {
  def getSourceField(source: String): Try[StructField] = {
    Try(df.schema.fields.filter(_.name == source).head)
  }

  def getType(sourceField: StructField): Try[StructType] = {
    Try(sourceField.dataType.asInstanceOf[StructType])
  }

  def genOutputCol(names: Array[String],source: String): Column = {
    f.struct(names.map(x => f.col(source).getItem(x).alias(x)): _*)
  }

  def dropFrom(source: String,toDrop: Array[String]): DataFrame = {
    getSourceField(source)
      .flatMap(getType)
      .map(_.fieldNames.diff(toDrop))
      .map(genOutputCol(_,source))
      .map(df.withColumn(source,_))
      .getOrElse(df)
  }
}

使用示例

scala> case class features(feat1: String,feat2: String,feat3: String)
defined class features

scala> case class record(label: String,features: features)
defined class record

scala> val df = sc.parallelize(Seq(record("a_label",features("f1","f2","f3")))).toDF
df: org.apache.spark.sql.DataFrame = [label: string,features: struct<feat1:string,feat2:string,feat3:string>]

scala> DFWithDropFrom(df).dropFrom("features",Array("feat1")).show
+-------+--------+
|  label|features|
+-------+--------+
|a_label| [f2,f3]|
+-------+--------+


scala> DFWithDropFrom(df).dropFrom("foobar",Array("feat1")).show
+-------+----------+
|  label|  features|
+-------+----------+
|a_label|[f1,f2,f3]|
+-------+----------+


scala> DFWithDropFrom(df).dropFrom("features",Array("foobar")).show
+-------+----------+
|  label|  features|
+-------+----------+
|a_label|[f1,f3]|
+-------+----------+

添加一个implicit conversion,你很好去.

（编辑：李大同）

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