Spark DataSet 、DataFrame 一些使用示例

以前使用过DS和DF，最近使用Spark ML跑实验，再次用到简单复习一下。

//案例数据
1,2,3
4,5,6
7,8,9
10,11,12
13,14,15
1,2,3
4,5,6
7,8,9
10,11,12
13,14,15
1,2,3
4,5,6
7,8,9
10,11,12
13,14,15

1：DS与DF关系？

type DataFrame = Dataset[Row]

2：加载txt数据

  val rdd = sc.textFile("data")

  val df = rdd.toDF()

这种直接生成DF，df数据结构为（查询语句：df.select("*").show(5)）：

只有一列，属性为value。

3： df.printSchema()

4：case class 可以直接就转成DS

// Note: Case classes in Scala 2.10 can support only up to 22 fields. To work around this limit,
// you can use custom classes that implement the Product interface
case class Person(name: String, age: Long)

// Encoders are created for case classes
val caseClassDS = Seq(Person("Andy", 32)).toDS()

5：直接解析主流格式文件

val path = "examples/src/main/resources/people.json"
val peopleDS = spark.read.json(path).as[Person]

6：RDD转成DataSet两种方法

数据格式:

xiaoming,18,iPhone
mali,22,xiaomi
jack,26,smartisan
mary,16,meizu
kali,45,huawei

（a）：使用反射推断模式

  val persons = rdd.map {
    x =>
      val fs = x.split(",")
      Person(fs(0), fs(1).toInt, fs(2))
  }

  persons.toDS().show(2)
  persons.toDF("newName", "newAge", "newPhone").show(2)
  persons.toDF().show(2)

（b）：编程方式指定模式

步骤：

import org.apache.spark.sql.types._
  //1:创建RDD
  val rddString = sc.textFile("C:\\Users\\Daxin\\Documents\\GitHub\\OptimizedRF\\sql_data")
  //2：创建schema
  val schemaString = "name age phone"
  val fields = schemaString.split(" ").map {
    filedName => StructField(filedName, StringType, nullable = true)
  }
  val schema = StructType(fields)
  //3：数据转成Row
  val rowRdd = rddString.map(_.split(",")).map(attributes => Row(attributes(0), attributes(1), attributes(2)))
  //创建DF
  val personDF = spark.createDataFrame(rowRdd, schema)
  personDF.show(5)

7：注册视图

  //全局表，生命周期多个session可以共享并且创建该视图的sparksession停止该视图也不会过期
  personDF.createGlobalTempView("GlobalTempView_Person")
  //临时表，存在的话覆盖。生命周期和sparksession相同
  personDF.createOrReplaceTempView("TempView_Person")
  //personDF.createTempView("TempView_Person") //如果视图已经存在则异常

  //  Global temporary view is tied to a system preserved database `global_temp`
  //全局视图存储在global_temp数据库中，如果不加数据库前缀异常，提示找不到视图
  spark.sql("select * from global_temp.GlobalTempView_Person").show(2)
  //临时表不需要添加数据库
  spark.sql("select * from TempView_Person").show(2)

8:UDF 定义：

Untyped User-Defined Aggregate Functions

package com.daxin.sq.df

import org.apache.spark.sql.expressions.MutableAggregationBuffer
import org.apache.spark.sql.expressions.UserDefinedAggregateFunction
import org.apache.spark.sql.types._
import org.apache.spark.sql.Row

/**
  * Created by Daxin on 2017/11/18.
  * url：http://spark.apache.org/docs/latest/sql-programming-guide.html#untyped-user-defined-aggregate-functions
  */

//Untyped User-Defined Aggregate Functions
object MyAverage extends UserDefinedAggregateFunction {

  // Data types of input arguments of this aggregate function
  override def inputSchema: StructType = StructType(StructField("inputColumn", IntegerType) :: Nil) //2

  // Updates the given aggregation buffer `buffer` with new input data from `input`
  //TODO  第一个缓冲区是sum，第二个缓冲区是元素个数
  override def update(buffer: MutableAggregationBuffer, input: Row): Unit = {
    if (!input.isNullAt(0)) {
      buffer(0) = buffer.getInt(0) + input.getInt(0) // input.getInt(0)是中inputSchema定义的第0个元素
      buffer(1) = buffer.getInt(1) + 1
      println()
    }
  }

  // Data types of values in the aggregation buffer
  //TODO  定义缓冲区的模型（也就是数据结构）
  override def bufferSchema: StructType = StructType(StructField("sum", IntegerType) :: StructField("count", IntegerType) :: Nil)

  // Merges two aggregation buffers and stores the updated buffer values back to `buffer1`
  //TODO MutableAggregationBuffer 是Row子类
  override def merge(buffer1: MutableAggregationBuffer, buffer2: Row): Unit = {
    //TODO 合并分区，将结果更新到buffer1
    buffer1(0) = buffer1.getInt(0) + buffer2.getInt(0)
    buffer1(1) = buffer1.getInt(1) + buffer2.getInt(1)

    println()
  }

  // Initializes the given aggregation buffer. The buffer itself is a `Row` that in addition to
  // standard methods like retrieving a value at an index (e.g., get(), getBoolean()), provides
  // the opportunity to update its values. Note that arrays and maps inside the buffer are still
  // immutable.
  override def initialize(buffer: MutableAggregationBuffer): Unit = {
    buffer(0) = 0
    buffer(1) = 0
  }

  // Whether this function always returns the same output on the identical input
  override def deterministic: Boolean = true

  // Calculates the final result
  override def evaluate(buffer: Row): Int = buffer.getInt(0) / buffer.getInt(1)

  // The data type of the returned value,返回值类型
  override def dataType: DataType = IntegerType //
}

测试代码：

  spark.udf.register("myAverage", MyAverage)
  val result = spark.sql("SELECT myAverage(age)  FROM TempView_Person")
  result.show()

8：关于机器学习中的DataFrame的schema定：

一列名字为 label，另一列名字为  features。一般可以使用case class完成转换

case class UDLabelpOint(label: Double, features: org.apache.spark.ml.linalg.Vector)