scala spark UDF 过滤器数组结构

Question

我有一个带架构的数据框

root
 |-- x: Long (nullable = false)
 |-- y: Long (nullable = false)
 |-- features: array (nullable = true)
 |    |-- element: struct (containsNull = true)
 |    |    |-- name: string (nullable = true)
 |    |    |-- score: double (nullable = true)

例如，我有数据

+--------------------+--------------------+------------------------------------------+
|                x   |              y     |       features                           |
+--------------------+--------------------+------------------------------------------+
|10                  |          9         |[["f1", 5.9], ["ft2", 6.0], ["ft3", 10.9]]|
|11                  |          0         |[["f4", 0.9], ["ft1", 4.0], ["ft2", 0.9] ]|
|20                  |          9         |[["f5", 5.9], ["ft2", 6.4], ["ft3", 1.9] ]|
|18                  |          8         |[["f1", 5.9], ["ft4", 8.1], ["ft2", 18.9]]|
+--------------------+--------------------+------------------------------------------+

我想用特定的前缀过滤特征，比如“ft”，所以最终我想要结果：

+--------------------+--------------------+-----------------------------+
|                x   |              y     |       features              |
+--------------------+--------------------+-----------------------------+
|10                  |          9         |[["ft2", 6.0], ["ft3", 10.9]]|
|11                  |          0         |[["ft1", 4.0], ["ft2", 0.9] ]|
|20                  |          9         |[["ft2", 6.4], ["ft3", 1.9] ]|
|18                  |          8         |[["ft4", 8.1], ["ft2", 18.9]]|
+--------------------+--------------------+-----------------------------+

我没有使用 Spark 2.4+，所以我不能使用这里提供的解决方案： Spark (Scala) filter array of structs without purge

我尝试使用 UDF，但仍然无效。 这是我的尝试。 我定义了一个 UDF：

def filterFeature: UserDefinedFunction = 
udf((features: Seq[Row]) =>
    features.filter{
        x.getString(0).startsWith("ft")
    }
)

但是如果我应用这个 UDF

df.withColumn("filtered", filterFeature($"features"))

我收到错误Schema for type org.apache.spark.sql.Row is not supported 。 我发现我无法从 UDF 返回Row 。 然后我试过了

def filterFeature: UserDefinedFunction = 
udf((features: Seq[Row]) =>
    features.filter{
        x.getString(0).startsWith("ft")
    }, (StringType, DoubleType)
)

然后我得到一个错误：

 error: type mismatch;
 found   : (org.apache.spark.sql.types.StringType.type, org.apache.spark.sql.types.DoubleType.type)
 required: org.apache.spark.sql.types.DataType
              }, (StringType, DoubleType)
                 ^

我还尝试了一些答案所建议的案例类：

case class FilteredFeature(featureName: String, featureScore: Double)
def filterFeature: UserDefinedFunction = 
udf((features: Seq[Row]) =>
    features.filter{
        x.getString(0).startsWith("ft")
    }, FilteredFeature
)

但我得到了：

 error: type mismatch;
 found   : FilteredFeature.type
 required: org.apache.spark.sql.types.DataType
              }, FilteredFeature
                 ^

我试过：

case class FilteredFeature(featureName: String, featureScore: Double)
def filterFeature: UserDefinedFunction = 
udf((features: Seq[Row]) =>
    features.filter{
        x.getString(0).startsWith("ft")
    }, Seq[FilteredFeature]
)

我有：

<console>:192: error: missing argument list for method apply in class GenericCompanion
Unapplied methods are only converted to functions when a function type is expected.
You can make this conversion explicit by writing `apply _` or `apply(_)` instead of `apply`.
              }, Seq[FilteredFeature]
                    ^

我试过：

case class FilteredFeature(featureName: String, featureScore: Double)
def filterFeature: UserDefinedFunction = 
udf((features: Seq[Row]) =>
    features.filter{
        x.getString(0).startsWith("ft")
    }, Seq[FilteredFeature](_)
)

我有：

<console>:201: error: type mismatch;
 found   : Seq[FilteredFeature]
 required: FilteredFeature
              }, Seq[FilteredFeature](_)
                          ^

在这种情况下我该怎么办？

Answer 1

你有两个选择：

a) 为 UDF 提供模式，这让您返回Seq[Row]

b) 将Seq[Row]转换为Tuple2的Seq或 case 类，则不需要提供模式（但如果使用元组，结构字段名称将丢失！）

对于您的情况，我更喜欢选项 a)（适用于具有许多字段的结构）：

val schema = df.schema("features").dataType

val filterFeature = udf((features:Seq[Row]) => features.filter(_.getAs[String]("name").startsWith("ft")),schema)

Answer 2

尝试这个：

def filterFeature: UserDefinedFunction =
    udf((features: Row) => {
      features.getAs[Array[Array[Any]]]("features").filter(in => in(0).asInstanceOf[String].startsWith("ft"))
 })

Answer 3

如果您不使用 Spark 2.4，那么这应该适用于您的情况

case class FilteredFeature(featureName: String, featureScore: Double)

import org.apache.spark.sql.functions._  
def filterFeature: UserDefinedFunction = udf((feature: Seq[Row]) => {
  feature.filter(x => {
    x.getString(0).startsWith("ft")
  }).map(r => FilteredFeature(r.getString(0), r.getDouble(1)))
})

df.select($"x", $"y", filterFeature($"feature") as "filter").show(false)

输出：

+---+---+-----------------------+
|x  |y  |filter                 |
+---+---+-----------------------+
|10 |9  |[[ft2,6.0], [ft3,10.9]]|
|11 |0  |[[ft1,4.0], [ft2,0.9]] |
|20 |9  |[[ft2,6.4], [ft3,1.9]] |
|18 |8  |[[ft4,8.1], [ft2,18.9]]|
+---+---+-----------------------+