[英]How to convert array type of dataset into string type in Apache Spark Java
[英]How to convert DataFrame to Dataset in Apache Spark in Java?
我可以很容易地將Scala中的DataFrame轉換為Dataset:
case class Person(name:String, age:Long)
val df = ctx.read.json("/tmp/persons.json")
val ds = df.as[Person]
ds.printSchema
但在Java版本中我不知道如何將Dataframe轉換為Dataset? 任何的想法?
我的努力是:
DataFrame df = ctx.read().json(logFile);
Encoder<Person> encoder = new Encoder<>();
Dataset<Person> ds = new Dataset<Person>(ctx,df.logicalPlan(),encoder);
ds.printSchema();
但是編譯器說:
Error:(23, 27) java: org.apache.spark.sql.Encoder is abstract; cannot be instantiated
基於@Leet-Falcon答案的解決方案:
DataFrame df = ctx.read().json(logFile);
Encoder<Person> encoder = Encoders.bean(Person.class);
Dataset<Person> ds = new Dataset<Person>(ctx, df.logicalPlan(), encoder);
官方Spark文檔在Dataset API中建議如下:
List<String> data = Arrays.asList("abc", "abc", "xyz");
Dataset<String> ds = context.createDataset(data, Encoders.STRING());
編碼器可以組成元組:
Encoder<Tuple2<Integer, String>> encoder2 = Encoders.tuple(Encoders.INT(), Encoders.STRING());
List<Tuple2<Integer, String>> data2 = Arrays.asList(new scala.Tuple2(1, "a");
Dataset<Tuple2<Integer, String>> ds2 = context.createDataset(data2, encoder2);
Encoders.bean(MyClass.class);
如果要將通用DF轉換為Java中的數據集,可以使用如下所示的RowEncoder類
DataFrame df = sql.read().json(sc.parallelize(ImmutableList.of(
"{\"id\": 0, \"phoneNumber\": 109, \"zip\": \"94102\"}"
)));
Dataset<Row> dataset = df.as(RowEncoder$.MODULE$.apply(df.schema()));
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