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淺談DataFrame和SparkSql取值誤區(qū)

 更新時(shí)間:2018年06月09日 08:57:14   作者:silentwolfyh  
今天小編就為大家分享一篇淺談DataFrame和SparkSql取值誤區(qū),具有很好的參考價(jià)值,希望對(duì)大家有所幫助。一起跟隨小編過來看看吧

1、DataFrame返回的不是對(duì)象。

2、DataFrame查出來的數(shù)據(jù)返回的是一個(gè)dataframe數(shù)據(jù)集。

3、DataFrame只有遇見Action的算子才能執(zhí)行

4、SparkSql查出來的數(shù)據(jù)返回的是一個(gè)dataframe數(shù)據(jù)集。

原始數(shù)據(jù)

scala> val parquetDF = sqlContext.read.parquet("hdfs://hadoop14:9000/yuhui/parquet/part-r-00004.gz.parquet")
df: org.apache.spark.sql.DataFrame = [timestamp: string, appkey: string, app_version: string, channel: string, lang: string, os_type: string, os_version: string, display: string, device_type: string, mac: string, network: string, nettype: string, suuid: string, register_days: int, country: string, area: string, province: string, city: string, event: string, use_interval_cat: string, use_duration_cat: string, use_interval: bigint, use_duration: bigint, os_upgrade_from: string, app_upgrade_from: string, page_name: string, event_name: string, error_type: string]

代碼

package DataFrame
import org.apache.spark.sql.SQLContext
import org.apache.spark.{SparkConf, SparkContext}
/**
 * Created by yuhui on 2016/6/14.
 */
object DataFrameTest {
 def main(args: Array[String]) {
 DataFrameInto()
 }
 def DataFrameInto() {
 val conf = new SparkConf()
 val sc = new SparkContext(conf)
 val sqlContext = new SQLContext(sc)
 val df = sqlContext.read.parquet("hdfs://hadoop14:9000/yuhui/parquet")
 //df.map(line => printinfo(line.getString(0)))
 //df.foreach(line => printinfo(line.getString(0)+" , "+line.getString(14)+" , "+line.getString(15)))
 //df.select("timestamp","country","area").foreach(line=>printinfo(line.toString))
 df.registerTempTable("infotable")
 sqlContext.sql("SELECT timestamp , country , area from infotable").foreach(line=>printinfo(line.toString))
 }
 def printinfo(msg: String) {println("printinfo函數(shù)-->" + msg) }
}

代碼解析

1、df.map(line => printinfo(line.getString(0)))

這段代碼不行執(zhí)行printinfo()函數(shù),因?yàn)橹挥衜ap算子,沒有Action算子。

2、df.foreach(line => printinfo(line.getString(0)+" , "+line.getString(14)+" , "+line.getString(15)))

通過Spark的Action算子接收數(shù)據(jù)進(jìn)行操作,執(zhí)行結(jié)果如下:

3、df.select("timestamp","country","area").foreach(line=>printinfo(line.toString))

通過DataFrame的API進(jìn)行操作,再通過Spark的Action算子打印出來,執(zhí)行結(jié)果如下:

4、sqlContext.sql("SELECT timestamp , country , area from infotable").foreach(line=>printinfo(line.toString))

執(zhí)行結(jié)果如下:

以上這篇淺談DataFrame和SparkSql取值誤區(qū)就是小編分享給大家的全部內(nèi)容了,希望能給大家一個(gè)參考,也希望大家多多支持腳本之家。

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