Spark 基础 —— 创建 DataFrame 的三种方式

1.自定义 schema（Rdd[Row] => DataSet[Row])

import org.apache.spark.sql.types._
val peopleRDD = spark.sparkContext.textFile("README.md")

val schemaString = "name age"
val fields = schemaString.split(" ")
.map(fieldName => StructField(fieldName, StringType, nullable = true))
val schema = StructType(fields)

val rowRDD = peopleRDD
.map(_.split(","))
.map(attributes => Row(attributes(0), attributes(1).trim))
rowRDD.collect().foreach(println)
val df = spark.createDataFrame(rowRDD, schema)

2.借助 case class 隐式转换（Rdd[Person] => DataSet[Row])

object DFTest {
  
  case class Person(name: String, age: Int)

  def main(args: Array[String]): Unit = {
    val spark = SparkSession
      .builder
      .appName("DataFrame Application").
      master("local")
      .getOrCreate()
    import spark.implicits._
    val peopleRDD = spark.sparkContext.textFile("README.md")

    val personRDD = peopleRDD
      .map(_.split(","))
      .map(attributes => Person(attributes(0), attributes(1).toInt))
    personRDD.collect().foreach(println)
    personRDD.toDF().show()
  }
}

3.直接从数据源创建

val df = spark
      .read
      .option("header", value = true)
      .csv("/home/lg/Documents/data/1987.csv")

此外　

spark.read.jdbc
spark.read.json
spark.read.parquet

233