scala:从csv中读取列为空值的数据

jdg4fx2g 于 2021-07-09 发布在 Spark

关注(0)|答案(2)|浏览(544)

环境-spark-3.0.1-bin-hadoop2.7、scalalibrarycontainer 2.12.3、scala、sparksql、eclipse-jee-oxygen-2-linux-gtk-x8664
我有一个csv文件，有3列数据类型：string，long，date。我已经将csv文件转换为datafram并想显示它。但它给出了以下错误

java.lang.ArrayIndexOutOfBoundsException: 2
at org.apache.spark.examples.sql.SparkSQLExample5$.$anonfun$runInferSchemaExample$2(SparkSQLExample5.scala:30)
at scala.collection.Iterator$$anon$10.next(Iterator.scala:448)
at scala.collection.Iterator$$anon$10.next(Iterator.scala:448)
at org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage1.processNext(Unknown Source)
at org.apache.spark.sql.execution.BufferedRowIterator.hasNext(BufferedRowIterator.java:43)
at org.apache.spark.sql.execution.WholeStageCodegenExec$$anon$1.hasNext(WholeStageCodegenExec.scala:729)
at org.apache.spark.sql.execution.SparkPlan.$anonfun$getByteArrayRdd$1(SparkPlan.scala:340)
at org.apache.spark.rdd.RDD.$anonfun$mapPartitionsInternal$2(RDD.scala:872)
at org.apache.spark.rdd.RDD.$anonfun$mapPartitionsInternal$2$adapted(RDD.scala:872)
at org.apache.spark.rdd.MapPartitionsRDD.compute(MapPartitionsRDD.scala:52)
at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:349)
at org.apache.spark.rdd.RDD.iterator(RDD.scala:313)
at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:90)
at org.apache.spark.scheduler.Task.run(Task.scala:127)
at org.apache.spark.executor.Executor$TaskRunner.$anonfun$run$3(Executor.scala:446)
at org.apache.spark.util.Utils$.tryWithSafeFinally(Utils.scala:1377)
at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:449)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)

在scala代码

.map(attributes => Person(attributes(0), attributes(1),attributes(2))).toDF();

如果后续行的值少于标头中的值数，则会出现错误。基本上，我正在尝试使用scala和spark从csv读取数据，其中列有空值。
行的列数不同。如果所有行都有3个列值，则它将成功运行。

package org.apache.spark.examples.sql

import org.apache.spark.sql.Row
import org.apache.spark.sql.SparkSession
import org.apache.spark.sql.types._
import java.sql.Date
import org.apache.spark.sql.functions._
import java.util.Calendar;

object SparkSQLExample5 {

 case class Person(name: String, age: String, birthDate: String)

 def main(args: Array[String]): Unit = {
val fromDateTime=java.time.LocalDateTime.now;
val spark = SparkSession.builder().appName("Spark SQL basic example").config("spark.master", "local").getOrCreate();
import spark.implicits._
runInferSchemaExample(spark);
spark.stop()
}

private def runInferSchemaExample(spark: SparkSession): Unit = {
import spark.implicits._
println("1. Creating an RDD of 'Person' object and converting into 'Dataframe' "+ 
    " 2. Registering the DataFrame as a temporary view.")
println("1. Third column of second row is not present.Last value of second row is comma.")
val peopleDF = spark.sparkContext
  .textFile("examples/src/main/resources/test.csv")
  .map(_.split(","))
  .map(attributes => Person(attributes(0), attributes(1),attributes(2))).toDF();
val finalOutput=peopleDF.select("name","age","birthDate")
finalOutput.show();
}

}
csv文件

col1,col2,col3
row21,row22,
row31,row32,

scala apache-spark apache-spark-sql

来源：https://stackoverflow.com/questions/66792984/scala-reading-data-from-csv-with-columns-have-null-values

2条答案

按热度按时间

2hh7jdfx1#

输入：csv文件

col1,col2,col3
row21,row22,
row31,row32,

代码：

import org.apache.spark.sql.SparkSession

object ReadCsvFile {

  case class Person(name: String, age: String, birthDate: String)

  def main(args: Array[String]): Unit = {
    val spark = SparkSession.builder().appName("Spark SQL basic example").config("spark.master", "local").getOrCreate();
    readCsvFileAndInferCustomSchema(spark);
    spark.stop()
  }

  private def readCsvFileAndInferCustomSchema(spark: SparkSession): Unit = {
    val df = spark.read.csv("C:/Users/Ralimili/Desktop/data.csv")
    val rdd = df.rdd.mapPartitionsWithIndex { (idx, iter) => if (idx == 0) iter.drop(1) else iter }
    val mapRdd = rdd.map(attributes => {
      Person(attributes.getString(0), attributes.getString(1),attributes.getString(2))
    })
    val finalDf = spark.createDataFrame(mapRdd)
    finalDf.show(false);
  }

}

输出

+-----+-----+---------+
|name |age  |birthDate|
+-----+-----+---------+
|row21|row22|null     |
|row31|row32|null     |
+-----+-----+---------+

如果要填充某些值而不是空值，请使用下面的代码

val customizedNullDf = finalDf.na.fill("No data")
 customizedNullDf.show(false);

输出

+-----+-----+---------+
|name |age  |birthDate|
+-----+-----+---------+
|row21|row22|No data  |
|row31|row32|No data  |
+-----+-----+---------+

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f87krz0w2#

在读取csv文件时尝试许可模式，它将为缺少的字段添加null val df = spark.sqlContext.read.format("csv").option("mode", "PERMISSIVE") .load("examples/src/main/resources/test.csv") 你可以找到更多的信息https://docs.databricks.com/data/data-sources/read-csv.html

赞(0）回复(0）举报 2021-07-09

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scala:从csv中读取列为空值的数据

2条答案

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