有没有办法从SparkSQL中的JSON文件中按顺序获取列名? [英] Is there a way to get the column names by order from a JSON file in SparkSQL ?

问题描述

我有一个JSON文件，并且当加载到Spark SQL中时，键将是我的专栏.现在，当我想检索列名时，它是按字母顺序检索的.但我希望细节应按其在文件中的显示顺序排列

I have a JSON file and the keys would be my column while loading into Spark SQL. Now when i want to retrieve the column names, it was retrieved in Alphabetical order. But i want the details should be in the order of how its present in the file

我的输入数据 是

{"id":1,"name":"Judith","email":"[e-mail]","city":"Évry","country":"France","ip":"199.63.123.157"}

下面是我检索列名并构建单个字符串的方法

Below is my way to retrieve the column names and build a single string

val dataframe = sqlContext.read.json("/virtual/home/587635/users.json")
    val columns = dataframe.columns 
    var query = columns.apply(0)+" STRING"  
    for (a <- 1 to (columns.length-1))
    {
      query = query + ","+ columns.apply(a) + " STRING" 
    }
    println(query)

这给了我类似下面的输出

This gives me the output like below

city STRING,country STRING,email STRING,id STRING,ip STRING,name STRING

但是我希望我的输出为

id STRING,name STRING,email STRING,city STRING,country STRING,ip STRING

推荐答案

添加select，其中列的顺序正确

Add a select with the columns correctly ordered

val dataframe = 
  sqlContext
    .read
    .json("/tmp/test.jsn")
    .select("id", "name", "email", "city", "country", "ip")

如果您在shell上尝试过此操作，则会注意到正确的顺序

If you tried this at the shell, you will notice the correct order

dataframe:org.apache.spark.sql.DataFrame = [id:bigint，名称:string， 电子邮件:字符串，城市:字符串，国家/地区:字符串，ip:字符串]

dataframe: org.apache.spark.sql.DataFrame = [id: bigint, name: string, email: string, city: string, country: string, ip: string]

通过执行脚本的其余部分，输出将达到预期的水平

By executing the rest of your script, the output is as expected

id STRING，名称STRING，电子邮件STRING，城市STRING，国家STRING，ip STRING

id STRING,name STRING,email STRING,city STRING,country STRING,ip STRING

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