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[英]How to add a new column to my DataFrame such that values of new column are populated by some other function in scala?
[英]About how to add a new column to an existing DataFrame with random values in Scala
我有一個帶有鑲木地板文件的數據框,我必須添加一個包含一些隨機數據的新列,但我需要這些隨機數據彼此不同。 這是我的實際代碼,spark 的當前版本是 1.5.1-cdh-5.5.2:
val mydf = sqlContext.read.parquet("some.parquet")
// mydf.count()
// 63385686
mydf.cache
val r = scala.util.Random
import org.apache.spark.sql.functions.udf
def myNextPositiveNumber :String = { (r.nextInt(Integer.MAX_VALUE) + 1 ).toString.concat("D")}
val myFunction = udf(myNextPositiveNumber _)
val myNewDF = mydf.withColumn("myNewColumn",lit(myNextPositiveNumber))
使用此代碼,我有以下數據:
scala> myNewDF.select("myNewColumn").show(10,false)
+-----------+
|myNewColumn|
+-----------+
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
+-----------+
看起來 udf myNextPositiveNumber 只被調用一次,不是嗎?
更新確認,只有一個不同的值:
scala> myNewDF.select("myNewColumn").distinct.show(50,false)
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
...
+-----------+
|myNewColumn|
+-----------+
|889488717D |
+-----------+
我做錯了什么?
更新 2:最后,在@user6910411 的幫助下,我得到了以下代碼:
val mydf = sqlContext.read.parquet("some.parquet")
// mydf.count()
// 63385686
mydf.cache
val r = scala.util.Random
import org.apache.spark.sql.functions.udf
val accum = sc.accumulator(1)
def myNextPositiveNumber():String = {
accum+=1
accum.value.toString.concat("D")
}
val myFunction = udf(myNextPositiveNumber _)
val myNewDF = mydf.withColumn("myNewColumn",lit(myNextPositiveNumber))
myNewDF.select("myNewColumn").count
// 63385686
更新 3
實際代碼生成如下數據:
scala> mydf.select("myNewColumn").show(5,false)
17/02/22 11:01:57 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
+-----------+
|myNewColumn|
+-----------+
|2D |
|2D |
|2D |
|2D |
|2D |
+-----------+
only showing top 5 rows
看起來 udf 函數只被調用一次,不是嗎? 我需要在該列中添加一個新的隨機元素。
更新 4 @user6910411
我有這個增加 id 的實際代碼,但它沒有連接最終的字符,這很奇怪。 這是我的代碼:
import org.apache.spark.sql.functions.udf
val mydf = sqlContext.read.parquet("some.parquet")
mydf.cache
def myNextPositiveNumber():String = monotonically_increasing_id().toString().concat("D")
val myFunction = udf(myNextPositiveNumber _)
val myNewDF = mydf.withColumn("myNewColumn",expr(myNextPositiveNumber))
scala> myNewDF.select("myNewColumn").show(5,false)
17/02/22 12:00:02 WARN Executor: 1 block locks were not released by TID = 1:
[rdd_4_0]
+-----------+
|myNewColumn|
+-----------+
|0 |
|1 |
|2 |
|3 |
|4 |
+-----------+
我需要類似的東西:
+-----------+
|myNewColumn|
+-----------+
|1D |
|2D |
|3D |
|4D |
+-----------+
火花 >= 2.3
可以使用asNondeterministic
方法禁用一些優化:
import org.apache.spark.sql.expressions.UserDefinedFunction
val f: UserDefinedFunction = ???
val fNonDeterministic: UserDefinedFunction = f.asNondeterministic
在使用此選項之前,請確保您了解這些保證。
火花 < 2.3
傳遞給udf 的函數應該是確定性的( SPARK-20586可能除外),並且空函數調用可以由常量替換。 如果要生成隨機數,請使用內置函數:
並轉換輸出以獲得所需的分布,例如:
(rand * Integer.MAX_VALUE).cast("bigint").cast("string")
您可以使用monotonically_increasing_id
來生成隨機值。
然后,您可以定義一個 UDF,在將其轉換為 String 后將任何字符串附加到它,因為monotonically_increasing_id
默認返回 Long。
scala> var df = Seq(("Ron"), ("John"), ("Steve"), ("Brawn"), ("Rock"), ("Rick")).toDF("names")
+-----+
|names|
+-----+
| Ron|
| John|
|Steve|
|Brawn|
| Rock|
| Rick|
+-----+
scala> val appendD = spark.sqlContext.udf.register("appendD", (s: String) => s.concat("D"))
scala> df = df.withColumn("ID",monotonically_increasing_id).selectExpr("names","cast(ID as String) ID").withColumn("ID",appendD($"ID"))
+-----+---+
|names| ID|
+-----+---+
| Ron| 0D|
| John| 1D|
|Steve| 2D|
|Brawn| 3D|
| Rock| 4D|
| Rick| 5D|
+-----+---+
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