Spark通过三种方式创建DataFrame-编程知识

Spark通过三种方式创建DataFrame

通过toDF方法创建DataFrame

通过toDF的方法创建

集合rdd中元素类型是样例类的时候，转成DataFrame之后列名默认是属性名
集合rdd中元素类型是元组的时候，转成DataFrame之后列名默认就是_N
集合rdd中元素类型是元组/样例类的时候，转成DataFrame(toDF(“ID”,“NAME”,“SEX”,“AGE6”))可以自定义列名

import org.apache.spark.sql.{DataFrame, SparkSession}
import org.junit.Testcase class Person(id:Int,name:String,sex:String,age:Int)
class TestScala {val spark = SparkSession.builder().appName("test").master("local[4]").getOrCreate()import spark.implicits._/*** 通过toDF的方法创建*    集合rdd中元素类型是样例类的时候，转成DataFrame之后列名默认是属性名*    集合rdd中元素类型是元组的时候，转成DataFrame之后列名默认就是_N*/@Testdef createDataFrameByToDF():Unit={//TODO 样例类是属性名val list = List(Person(1,"zhangsan","man",10),Person(2,"zhang2","woman",66),Person(3,"zhang3","man",70),Person(4,"zhang4","man",22))//需要隐士转换val df:DataFrame = list.toDF()df.show()//TODO 元祖是_Nval list2 = List((1,"zhangsan","man",10),(1,"zhang2","woman",66),(1,"zhang3","man",70),(1,"zhang4","man",22))//需要隐士转换val df1:DataFrame = list2.toDF()df1.show()//TODO 自定义属性名val list3 = List((1,"zhangsan","man",10),(1,"zhang2","woman",66),(1,"zhang3","man",70),(1,"zhang4","man",22))//需要隐士转换val df2:DataFrame = list3.toDF("ID","NAME","SEX","AGE6")df2.show()}}

结果
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通过读取文件创建DataFrame

json数据

{"age":20,"name":"qiaofeng"}
{"age":19,"name":"xuzhu"}
{"age":18,"name":"duanyu"}

  /*** 通过读取文件创建*/@Testdef createDataFrame():Unit={val df = spark.read.json("src/main/resources/user.json")df.show()}

通过createDataFrame方法创建DF

  @Testdef createDataFrameByMethod():Unit={val fields = Array(StructField("id",IntegerType),StructField("name",StringType),StructField("sex",StringType),StructField("age",IntegerType))val schema = StructType(fields)val rdd = spark.sparkContext.parallelize(List(Row(1, "zhangsan", "man", 10), Row(2, "zhang2", "woman", 66), Row(3, "zhang3", "man", 70), Row(4, "zhang4", "man", 22)))val df = spark.createDataFrame(rdd, schema)df.show()}