java - 如何使用 Java 在 Apache spark 中将一行数组平面映射为多行？

Question

我有一个 json 数据文件，其中包含一个属性，即“标签”的字符串数组。 Apache Spark DataFrame 架构如下所示:

root
 |-- acceptedAnswerId: long (nullable = true)
 |-- answerCount: long (nullable = true)
 |-- body: string (nullable = true)
 |-- score: long (nullable = true)
 |-- <b>tags</b>: array (nullable = true)
 |    |-- element: string (containsNull = true)
 |-- title: string (nullable = true)
 |-- viewCount: long (nullable = true)

我想在 Java 中将每一行分解成几行。我可以使用 Scala 找到类似的答案但无法用 Java 转换解决方案。有什么建议吗？

JSON 中的“标签”属性如下所示:

"tags":["c#",".net","compression","decompression"]

Answer 1

为了使解决方案更直观，示例 json 数据如下所示:

{"id":4,"score":358,"viewCount":24247,"answerCount":13,"commentCount":1,"favoriteCount":28,"tags":["c#","winforms","type-conversion","opacity"]}

下面是将 json 数据读取为“DataFrame”对象的 Java 代码片段:

JavaSparkContext sc = new JavaSparkContext(conf);
SQLContext sqlContext = new SQLContext(sc);

String jsonData = "{\"id\":4,\"score\":358,\"viewCount\":24247,\"tags\":[\"c#\",\"winforms\",\"type-conversion\",\"opacity\"]}";    
    
List dataSet = Arrays.asList(jsonData);

JavaRDD distData = sc.parallelize(dataSet);

DataFrame stackoverflow_Posts = sqlContext.read().json(distData);

stackoverflow_Posts.printSchema(); //let's print out the DataFrame schema (Output#1)

stackoverflow_Posts.show(); //let's show the DataFrame content (Ouput#2)

架构:Output#1 如下所示:

root
 |-- id: long (nullable = true)
 |-- score: long (nullable = true)
 |-- tags: array (nullable = true)
 |    |-- element: string (containsNull = true)
 |-- viewCount: long (nullable = true)

数据:Output#2 如下所示:

+---+-----+--------------------+---------+
| id|score|                tags|viewCount|
+---+-----+--------------------+---------+
|  4|  358|[c#, winforms, ty...|    24247|
+---+-----+--------------------+---------+

基于zero323的信息，我继续处理:

DataFrame expanded = stackoverflow_Posts.withColumn("tag", org.apache.spark.sql.functions.explode(stackoverflow_Posts.col("tags")));
        
expanded.printSchema(); //let's print out the DataFrame schema again (Output#3)
        
expanded.show(); //let's show the DataFrame content (Output#4)

架构:Output#3 如下所示:

root
 |-- id: long (nullable = true)
 |-- score: long (nullable = true)
 |-- tags: array (nullable = true)
 |    |-- element: string (containsNull = true)
 |-- viewCount: long (nullable = true)
 |-- tag: string (nullable = true)

爆炸后的数据:Output#4

+---+-----+--------------------+---------+---------------+
| id|score|                tags|viewCount|            tag|
+---+-----+--------------------+---------+---------------+
|  4|  358|[c#, winforms, ty...|    24247|             c#|
|  4|  358|[c#, winforms, ty...|    24247|       winforms|
|  4|  358|[c#, winforms, ty...|    24247|type-conversion|
|  4|  358|[c#, winforms, ty...|    24247|        opacity|
+---+-----+--------------------+---------+---------------+

结果看起来非常类似于使用 SQL 连接两个表。