如何在数据帧中引用广播变量 [英] How to refer broadcast variable in dataframes

问题描述

我用的是spark1.6.我尝试广播 RDD，但不确定如何访问数据帧中的广播变量?

我有两个数据框员工 &部门.

员工数据框

-------------------员工 ID |员工姓名 |Emp_Age------------------1 |约翰 |252 |大卫 |35

部门数据框

--------------------部门 ID |部门名称 |员工编号-----------------------------1 |管理员 |12 |人力资源 |2导入 scala.collection.Mapval df_emp = hiveContext.sql("select * from emp")val df_dept = hiveContext.sql("select * from dept")val rdd = df_emp.rdd.map(row => (row.getInt(0),row.getString(1)))val lkp = rdd.collectAsMap()val bc = sc.broadcast(lkp)打印(bc.value.get(1).get)--以下语句不起作用val combineDF = df_dept.withColumn("emp_name",bc.value.get($"emp_id").get)

1. 如何在上述组合DF语句中引用广播变量?
2. 如果 lkp 没有返回任何值，如何处理?
3. 有没有办法从 lkp 返回多条记录(假设在查找中 emp_id=1 有 2 条记录，我想获得两条记录)
4. 如何从广播中返回多个值...(emp_name & emp_age)

解决方案

如何在上面的combinedDF语句中引用广播变量?

使用udf.如果 emp_id 是 Int

val f = udf((emp_id: Int) => bc.value.get(emp_id))df_dept.withColumn("emp_name", f($"emp_id"))

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lkp没有返回值怎么处理?

不要使用如上所示的get

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有没有办法从lkp返回多条记录

使用groupByKey:

val lkp = rdd.groupByKey.collectAsMap()

和爆炸:

df_dept.withColumn("emp_name", f($"emp_id")).withColumn("emp_name",explode($"emp_name"))

或者只是跳过所有步骤并广播:

import org.apache.spark.sql.functions._df_emp.join(broadcast(df_dep), Seq("Emp Id"), "left")

I use spark1.6. I tried to broadcast a RDD and am not sure how to access the broadcasted variable in the data frames?

I have two dataframes employee & department.

Employee Dataframe

-------------------
Emp Id | Emp Name | Emp_Age
------------------
1 | john | 25

2 | David | 35

Department Dataframe

--------------------
Dept Id | Dept Name | Emp Id
-----------------------------
1 | Admin | 1

2 | HR | 2

import scala.collection.Map

val df_emp = hiveContext.sql("select * from emp")

val df_dept = hiveContext.sql("select * from dept")

val rdd = df_emp.rdd.map(row => (row.getInt(0),row.getString(1)))

val lkp = rdd.collectAsMap()

val bc = sc.broadcast(lkp)

print(bc.value.get(1).get)

--Below statement doesn't work

val combinedDF = df_dept.withColumn("emp_name",bc.value.get($"emp_id").get)

1. How do I refer the broadcast variable in the above combinedDF statement?
2. How to handle if the lkp doesn't return any value?
3. Is there a way to return multiple records from the lkp (lets assume if there are 2 records for emp_id=1 in the look up, I would like to get both records)
4. How to return more than one value from broadcast...(emp_name & emp_age)

解决方案

How do I refer the broadcast variable in the above combinedDF statement?

Use udf. If emp_id is Int

val f = udf((emp_id: Int) =>  bc.value.get(emp_id))

df_dept.withColumn("emp_name", f($"emp_id"))

How to handle if the lkp doesn't return any value?

Don't use get as shown above

Is there a way to return multiple records from the lkp

Use groupByKey:

val lkp = rdd.groupByKey.collectAsMap()

and explode:

df_dept.withColumn("emp_name", f($"emp_id")).withColumn("emp_name", explode($"emp_name"))

or just skip all the steps and broadcast:

import org.apache.spark.sql.functions._

df_emp.join(broadcast(df_dep), Seq("Emp Id"), "left")

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