加入一个数据帧spark java

首先,感谢您抽出时间阅读我的问题.

我的问题如下：在Spark with Java中,我在两个数据帧中加载了两个csv文件的数据.

这些数据框将具有以下信息.

Dataframe机场

Id | Name    | City
-----------------------
1  | Barajas | Madrid

Dataframe airport_city_state

City | state
----------------
Madrid | España

我想加入这两个数据帧,使它看起来像这样：

数据帧结果

Id | Name    | City   | state
--------------------------
1  | Barajas | Madrid | España

其中dfairport.city = dfaiport_city_state.city

但是我无法用语法来澄清所以我可以正确地进行连接.我如何创建变量的一些代码：

 // Load the csv, you have to specify that you have header and what delimiter you have
Dataset <Row> dfairport = Load.Csv (sqlContext, data_airport);
Dataset <Row> dfairport_city_state = Load.Csv (sqlContext,   data_airport_city_state);


// Change the name of the columns in the csv dataframe to match the columns in the database
// Once they match the name we can insert them
Dfairport
.withColumnRenamed ("leg_key", "id")
.withColumnRenamed ("leg_name", "name")
.withColumnRenamed ("leg_city", "city")

dfairport_city_state
.withColumnRenamed("city", "ciudad")
.withColumnRenamed("state", "estado");

解决方法:

您可以使用带有列名的join方法来连接两个数据帧,例如：

Dataset <Row> dfairport = Load.Csv (sqlContext, data_airport);
Dataset <Row> dfairport_city_state = Load.Csv (sqlContext,   data_airport_city_state);

Dataset <Row> joined = dfairport.join(dfairport_city_state, dfairport_city_state("City"));

还有一个重载版本,允许您将连接类型指定为第三个参数,例如：

数据集< Row>加入= dfairport.join(dfairport_city_state,dfairport_city_state(“City”),“left_outer”);

Here更多关于加入.

标签：java,dataframe,apache-spark,spark-dataframe
来源： https://codeday.me/bug/20190716/1474608.html