RDD&Dataset&DataFrame

Dataset创建

object DatasetCreation {
  def main(args: Array[String]): Unit = {
    val spark = SparkSession
      .builder()
      .appName("SparkSessionTest")
      .getOrCreate()

    import spark.implicits._

    //1: range
    val ds1 = spark.range(0, 10, 2, 2)
    ds1.show()

    val dogs = Seq(Dog("jitty", "red"), Dog("mytty", "yellow"))
    val cats = Seq(new Cat("jitty", 2), new Cat("mytty", 4))

    //2: 从Seq[T]中创建
    val data = dogs
    val ds = spark.createDataset(data)
    ds.show()

    //3: 从RDD[T]中创建
    val dogRDD = spark.sparkContext.parallelize(dogs)
    val dogDS = spark.createDataset(dogRDD)
    dogDS.show()

    val catRDD = spark.sparkContext.parallelize(cats)
    //val catDSWithoutEncoder = spark.createDataset(catRDD)
    val catDS = spark.createDataset(catRDD)(Encoders.bean(classOf[Cat]))
    catDS.show()

    //Encoders 负责JVM对象类型与spark SQL内部数据类型之间的转换
    val intDs = Seq(1, 2, 3).toDS() // implicitly provided (spark.implicits.newIntEncoder)
    val seqIntDs = Seq(Seq(1), Seq(2), Seq(3)).toDS() // implicitly provided (spark.implicits.newIntSeqEncoder)
    val arrayIntDs = Seq(Array(1), Array(2), Array(3)).toDS() // implicitly provided (spark.implicits.newIntArrayEncoder)

    //支持的Encoders有如下：
    Encoders.product //tuples and case classes
    Encoders.scalaBoolean
    Encoders.scalaByte
    Encoders.scalaDouble
    Encoders.scalaFloat
    Encoders.scalaInt
    Encoders.scalaLong
    Encoders.scalaShort

    Encoders.bean(classOf[Cat])

    spark.stop()
  }
}

　　

DataFrame创建

import org.apache.spark.sql.types.{IntegerType, StringType, StructField, StructType}
import org.apache.spark.sql.{Row, SparkSession}

object DataFrameCreation {
  def main(args: Array[String]): Unit = {
    val spark = SparkSession
      .builder()
      .appName("SparkSessionTest")
      .getOrCreate()

    //1: 从RDD[A <: Product]中创建, case class 和 tuple都是Product的子类
    val rdd = spark.sparkContext.textFile("").map(line => {
      val splitData = line.split(",")
      Dog(splitData(0), splitData(1))
    })

    val tupleRDD = spark.sparkContext.parallelize(Seq(("jitty", 2), ("mytty", 4)))

    spark.createDataFrame(rdd)
    spark.createDataFrame(tupleRDD)

    val dogRDD = spark.sparkContext.parallelize(Seq(Dog("jitty", "red"), Dog("mytty", "yellow")))
    val dogDf = spark.createDataFrame(dogRDD)
    dogDf.show()

    //2: 从Seq[A <: Product]中创建
    val dogSeq = Seq(Dog("jitty", "red"), Dog("mytty", "yellow"))
    spark.createDataFrame(dogSeq).show()

    //3:用RDD[_] + class创建，这个class是java的bean
    val catRDD = spark.sparkContext.parallelize(Seq(new Cat("jitty", 2), new Cat("mytty", 4)))
    //val catDf = spark.createDataFrame(catRDD)
    val catDf = spark.createDataFrame(catRDD, classOf[Cat])
    catDf.show()
    catDf.createOrReplaceTempView("cat")
    spark.sql("select * from cat").show() //需要注意的是查询出来的cat的属性的顺序是不固定的

    //4: 用RDD[Row] + schema创建
    val rowSeq = Seq("tom,30", "katy, 46").map(_.split(",")).map(p => Row(p(0), p(1).trim.toInt))
    val rowRDD = spark.sparkContext.parallelize(rowSeq)
    val schema =
          StructType(
              StructField("name", StringType, false) ::
                StructField("age", IntegerType, true) :: Nil)
    val dataFrame = spark.createDataFrame(rowRDD, schema)
    dataFrame.printSchema
    dataFrame.show()

    //5: 从外部数据源中创建
    val df = spark.read.json(s"${BASE_PATH}/IoT_device_info.json")
    df.show()

    spark.stop()
  }
}

　　

RDD&Dataset&DataFrame的转换

package com.twq.dataset.creation
import com.twq.dataset.Dog
import org.apache.spark.rdd.RDD
import org.apache.spark.sql.{Row, SparkSession}

object RDDDatasetTransform {
  def main(args: Array[String]): Unit = {
    val spark = SparkSession
      .builder()
      .appName("RDDDatasetTransform")
      .getOrCreate()

    val dogs = Seq(Dog("jitty", "red"), Dog("mytty", "yellow"))

    val dogRDD = spark.sparkContext.parallelize(dogs)

    //1: RDD转DataFrame
    import spark.implicits._
    val dogDF = dogRDD.toDF()
    dogDF.show()

    val renameSchemaDF = dogRDD.toDF ("first_name", "lovest_color")
    renameSchemaDF.show()

    //2: DataFrame转RDD, schema信息丢掉了
    val dogRowRDD: RDD[Row] = dogDF.rdd
    dogRowRDD.collect()
    renameSchemaDF.rdd.collect()

    //3: RDD转Dataset
    val dogDS = dogRDD.toDS()
    dogDS.show()

    //4: Dataset转RDD
    val dogRDDFromDs: RDD[Dog] = dogDS.rdd
    dogRDDFromDs.collect()

    //5: DataFrame转Dataset
    val dogDsFromDf = dogDF.as[Dog]
    dogDsFromDf.show()

    //6: Dataset转DataFrame
    val dogDfFromDs = dogDsFromDf.toDF()
    dogDfFromDs.show()

    spark.stop()
  }
}

　　

schema的定义以及复杂数据类型的用法

import org.apache.spark.sql.types._
import org.apache.spark.sql.{Row, SaveMode, SparkSession}

object SchemaApiTest {
  def main(args: Array[String]): Unit = {
    val spark = SparkSession
      .builder()
      .appName("SchemaApiTest")
      .master("local")
      .getOrCreate()

    val iotDeviceDf = spark.read.json(s"${BASE_PATH}/IoT_device_info.json")

    iotDeviceDf.toString()

    //1: schema的展示
    iotDeviceDf.schema
    iotDeviceDf.printSchema()

    //2: schema中可以有复杂数据类型
    val schema =
      StructType(
        StructField("name", StringType, false) ::
          StructField("age", IntegerType, true) ::
          StructField("map", MapType(StringType, StringType), true) ::
          StructField("array", ArrayType(StringType), true) ::
          StructField("struct",
            StructType(Seq(StructField("field1", StringType), StructField("field2", StringType))))
          :: Nil)

    val people =
      spark.sparkContext.parallelize(Seq("tom,30", "katy, 46")).map(_.split(",")).map(p =>
        Row(p(0), p(1).trim.toInt, Map(p(0) -> p(1)), Seq(p(0), p(1)), Row("value1", "value2")))
    val dataFrame = spark.createDataFrame(people, schema)
    dataFrame.printSchema
    dataFrame.show()

    dataFrame.select("map").collect().map(row => row.getAs[Map[String, String]]("map"))
    dataFrame.select("array").collect().map(row => row.getAs[Seq[String]]("array"))
    dataFrame.select("struct").collect().map(row => row.getAs[Row]("struct"))

    //schema 的用处
    val exampleSchema = new StructType().add("name", StringType).add("age", IntegerType)
    exampleSchema("name")   ///提取name信息，类型
    exampleSchema.fields  //所有字段类型信息
    exampleSchema.fieldNames//   所有字段名字
    exampleSchema.fieldIndex("name")///  字段索引位置

    //1：查看一个parquet文件的schema
    val sessionDf = spark.read.parquet(s"${BASE_PATH}/trackerSession")
    sessionDf.schema
    sessionDf.printSchema()

    //2：比对两个parquet文件的schema是否相同
    val changedSchemaFieldNames = sessionDf.schema.fieldNames.map(fieldName => {
      if (fieldName == "pageview_count") {
        "pv_count"
      } else fieldName
    })
    sessionDf.toDF(changedSchemaFieldNames:_*).write.mode(SaveMode.Overwrite).parquet(s"${BASE_PATH}/trackerSession_changeSchema")
    val schemaChangeSessionDf = spark.read.parquet(s"${BASE_PATH}/trackerSession_changeSchema")
    schemaChangeSessionDf.schema
    schemaChangeSessionDf.printSchema()

    val oldSchema = sessionDf.schema

    val changeSchema = schemaChangeSessionDf.schema

    oldSchema == changeSchema //false

    //3：两个parquet文件的schema不一样，需要进行统一
    val allSessionError
      = spark.read.parquet(s"${BASE_PATH}/trackerSession", s"${BASE_PATH}/trackerSession_changeSchema")
    allSessionError.printSchema()
    allSessionError.show()

    val allSessionRight = sessionDf.toDF(changeSchema.fieldNames:_*).union(schemaChangeSessionDf)
    allSessionRight.printSchema()
    allSessionRight.show()

    spark.stop()

  }
}