Spark 创建Dataframe和创建空的DataFrame

 创建空的DataFrame

var ret = spark.emptyDataFrame

1. 隐式转换toDF

1）使用case-class

引入隐式转换的包

import sqlContext.implicits._

创建case-class的Rdd

    val rdd: RDD[Person] = sc.parallelize(Array(
      Person("fanghailiang", 29),
      Person("sunyu", 28),
      Person("jiaolu", 26),
      Person("dingzelin", 31)
    ))

转换成DataFrame

val df: DataFrame = rdd.toDF()

2）将二元数组直接转换为DataFrame

val rdd2: RDD[(String, Int)] = sc.parallelize(Array(
    ("fanghailiang", 29),
    ("sunyu", 28),
    ("jiaolu", 26),
    ("dingzelin", 31)
))
 
val df2: DataFrame = rdd2.toDF("name2", "age3")

2.通过RowRdd+Scheme

1, 构建RowRdd

    val rowRdd: RDD[Row] = sc.parallelize(Array(
      ("fanghailiang", 29),
      ("sunyu", 28),
      ("jiaolu", 26),
      ("dingzelin", 31)
    )).map{
      case (name, age) => {
        Row(name, age)
      }
    }

2. 构建scheme

    val schema: StructType = StructType(Array(
      StructField("name", StringType, false),
      StructField("age", IntegerType, false)
    ))

3. 创建DataFrame 

val df3: DataFrame = sqlContext.createDataFrame(rowRdd, schema)