数据框查找和优化

Question

我在Java中使用spark-sql-2.4.3v。 我有下面的情况

+---+-----+-------+------+-----+
| id| code|entity|value1|value2|
+---+-----+-------+------+-----+
| 20|score|school|     a|   aaa|
| 21|score|school|    aa|    aa|
| 22| rate|school|    11|    14|
| 23|score|school|  aaaa|     a|
| 24| rate|school|    12|    12|
| 25|score|school|  aaaa|     a|
+---+-----+------+------+------+

我只需要对最终输出中的“代码”与“值”进行映射，仅适用于在“数据”数据框中具有“代码”作为“得分”的那些行/记录。

如何从codeValudeDf中查找哈希图，以便获得如下输出

{{1}}

是否有可能使此查询最佳化，即每次我都不应该从DB中提取数据帧数据时？

Answer 1

如果查找数据的大小较小，则可以创建Map和broadcast。 broadcasted map可以在udf中轻松使用，如下所示-

加载提供的测试数据

 val data = List(
      ("20", "score", "school",  14 ,12),
      ("21", "score", "school",  13 , 13),
      ("22", "rate", "school",  11 ,14),
      ("23", "score", "school",  11 ,14),
      ("24", "rate", "school",  12 ,12),
      ("25", "score", "school", 11 ,14)
    )
    val df = data.toDF("id", "code", "entity", "value1","value2")
    df.show
    /**
      * +---+-----+------+------+------+
      * | id| code|entity|value1|value2|
      * +---+-----+------+------+------+
      * | 20|score|school|    14|    12|
      * | 21|score|school|    13|    13|
      * | 22| rate|school|    11|    14|
      * | 23|score|school|    11|    14|
      * | 24| rate|school|    12|    12|
      * | 25|score|school|    11|    14|
      * +---+-----+------+------+------+
      */

    //this look up data populated from DB.

    val ll = List(
      ("aaaa", 11),
      ("aaa", 12),
      ("aa", 13),
      ("a", 14)
    )
    val codeValudeDf = ll.toDF( "code", "value")
    codeValudeDf.show
    /**
      * +----+-----+
      * |code|value|
      * +----+-----+
      * |aaaa|   11|
      * | aaa|   12|
      * |  aa|   13|
      * |   a|   14|
      * +----+-----+
      */

broadcasted map可以在udf中轻松使用，如下所示-

    val lookUp = spark.sparkContext
      .broadcast(codeValudeDf.map{case Row(code: String, value: Integer) => value -> code}
      .collect().toMap)

    val look_up = udf((value: Integer) => lookUp.value.get(value))

    df.withColumn("value1",
      when($"code" === "score", look_up($"value1")).otherwise($"value1".cast("string")))
      .withColumn("value2",
        when($"code" === "score", look_up($"value2")).otherwise($"value2".cast("string")))
      .show(false)
    /**
      * +---+-----+------+------+------+
      * |id |code |entity|value1|value2|
      * +---+-----+------+------+------+
      * |20 |score|school|a     |aaa   |
      * |21 |score|school|aa    |aa    |
      * |22 |rate |school|11    |14    |
      * |23 |score|school|aaaa  |a     |
      * |24 |rate |school|12    |12    |
      * |25 |score|school|aaaa  |a     |
      * +---+-----+------+------+------+
      */

Answer 2

使用广播的地图确实是一个明智的决定，因为您无需每次都访问数据库即可提取查找数据。

在这里，我已经使用UDF中的键值映射解决了该问题。我无法比较它的性能广播地图方法，但欢迎火花专家发表意见。

步骤＃1：构建KeyValueMap-

val data = List(
  ("20", "score", "school",  14 ,12),
  ("21", "score", "school",  13 , 13),
  ("22", "rate", "school",  11 ,14),
  ("23", "score", "school",  11 ,14),
  ("24", "rate", "school",  12 ,12),
  ("25", "score", "school", 11 ,14)
 )
val df = data.toDF("id", "code", "entity", "value1","value2")

val ll = List(
   ("aaaa", 11),
  ("aaa", 12),
  ("aa", 13),
  ("a", 14)
 )
val codeValudeDf = ll.toDF( "code", "value")


val Keys = codeValudeDf.select("value").collect().map(_(0).toString).toList

val Values = codeValudeDf.select("code").collect().map(_(0).toString).toList
val KeyValueMap = Keys.zip(Values).toMap

步骤＃2：创建UDF

def CodeToValue(code: String, key: String): String = { 
if (key == null) return ""
if (code != "score") return key
val result: String = KeyValueMap.getOrElse(key,"not found!") 
return result }

val CodeToValueUDF = udf (CodeToValue(_:String, _:String):String )

第3步：在原始数据框中使用UDF添加派生列

val newdf  = df.withColumn("Col1", CodeToValueUDF(col("code"), col("value1")))

val finaldf = newdf.withColumn("Col2", CodeToValueUDF(col("code"), col("value2")))
    
finaldf.show(false)

+---+-----+------+------+------+----+----+
| id| code|entity|value1|value2|Col1|Col2|
+---+-----+------+------+------+----+----+
| 20|score|school|    14|    12|   a| aaa|
| 21|score|school|    13|    13|  aa|  aa|
| 22| rate|school|    11|    14|  11|  14|
| 23|score|school|    11|    14|aaaa|   a|
| 24| rate|school|    12|    12|  12|  12|
| 25|score|school|    11|    14|aaaa|   a|
+---+-----+------+------+------+----+----+