Spark(Scala)在for循环内执行数据框 [英] Spark (Scala) execute dataframe within for loop

问题描述

我正在使用spark 1.6.1版本.我需要循环执行数据框.

I am using spark 1.6.1 version. I have requirement to execute dataframe in loop.

for ( i <- List ('a','b')){
 val i = sqlContext.sql("SELECT i, col1, col2 FROM DF1")}

我希望此数据帧执行两次(i = a和i = b).

I want this dataframe to be executed twice (i = a and i = b).

推荐答案

您的代码几乎正确. 除了两件事:

Your code is almost correct. Except two things :

• i已在您的for循环中使用，因此请不要在val i =
中使用它
• 如果要在字符串中使用i的值，请使用字符串插值"

• i is already used in your for loop so don't use it in val i =
• If you want to use the value of i in a string, use String Interpolation

因此您的代码应类似于:

So your code should look like :

for (i <- List ('a','b')) {
  val df = sqlContext.sql(s"SELECT $i, col1, col2 FROM DF1")
  df.show()
}

---

作者评论后

您可以先使用.map然后使用.reduceLeft来完成此操作:

You can do this with a .map and then a .reduceLeft :

// All your dataframes
val dfs = Seq('a','b').map { i =>
  sqlContext.sql(s"SELECT $i, col1, col2 FROM DF1")
}

// Then you can reduce your dataframes into one
val unionDF = dfs.reduceLeft((dfa, dfb) => 
  dfa.unionAll(dfb)
)

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