Apache Spark 数据集 API - 不接受架构 StructType

Question

我有以下 class 使用 Spark 数据加载无头 CSV 文件 API。

我遇到的问题是我无法让 SparkSession 接受应该定义每一列的架构 StructType。结果数据框是字符串类型的未命名列

public class CsvReader implements java.io.Serializable {

public CsvReader(StructType builder) {
        this.builder = builder;
    }
private StructType builder;

SparkConf conf = new SparkConf().setAppName("csvParquet").setMaster("local");
// create Spark Context
SparkContext context = new SparkContext(conf);
// create spark Session
SparkSession sparkSession = new SparkSession(context);

Dataset<Row> df = sparkSession
        .read()
        .format("com.databricks.spark.csv")
        .option("header", false)
        //.option("inferSchema", true)
        .schema(builder)
        .load("/Users/Chris/Desktop/Meter_Geocode_Data.csv"); //TODO: CMD line arg

public void printSchema() {
    System.out.println(builder.length());
    df.printSchema();
}

public void printData() {
    df.show();
}

public void printMeters() {
    df.select("meter").show();
}

public void printMeterCountByGeocode_result() {
    df.groupBy("geocode_result").count().show();
}

public Dataset getDataframe() {
            return df;
 }

}

生成的数据框架构是：

root
 |-- _c0: string (nullable = true)
 |-- _c1: string (nullable = true)
 |-- _c2: string (nullable = true)
 |-- _c3: string (nullable = true)
 |-- _c4: string (nullable = true)
 |-- _c5: string (nullable = true)
 |-- _c6: string (nullable = true)
 |-- _c7: string (nullable = true)
 |-- _c8: string (nullable = true)
 |-- _c9: string (nullable = true)
 |-- _c10: string (nullable = true)
 |-- _c11: string (nullable = true)
 |-- _c12: string (nullable = true)
 |-- _c13: string (nullable = true)

调试器显示 'builder' StrucType 已正确定义：

0 = {StructField@4904} "StructField(geocode_result,DoubleType,false)"
1 = {StructField@4905} "StructField(meter,StringType,false)"
2 = {StructField@4906} "StructField(orig_easting,StringType,false)"
3 = {StructField@4907} "StructField(orig_northing,StringType,false)"
4 = {StructField@4908} "StructField(temetra_easting,StringType,false)"
5 = {StructField@4909} "StructField(temetra_northing,StringType,false)"
6 = {StructField@4910} "StructField(orig_address,StringType,false)"
7 = {StructField@4911} "StructField(orig_postcode,StringType,false)"
8 = {StructField@4912} "StructField(postcode_easting,StringType,false)"
9 = {StructField@4913} "StructField(postcode_northing,StringType,false)"
10 = {StructField@4914} "StructField(distance_calc_method,StringType,false)"
11 = {StructField@4915} "StructField(distance,StringType,false)"
12 = {StructField@4916} "StructField(geocoded_address,StringType,false)"
13 = {StructField@4917} "StructField(geocoded_postcode,StringType,false)"

我做错了什么？非常感谢任何帮助！

Answer 1

如果你想通过builder.Or初始化它，你应该把你的df放在构造函数中你可以把它放在一个成员函数中。

Answer 2

定义变量 Dataset<Row> df 并将用于读取 CSV 文件的代码块移动到 getDataframe() 方法中，如下所示。

private Dataset<Row> df = null;

public Dataset getDataframe() {
    df = sparkSession
        .read()
        .format("com.databricks.spark.csv")
        .option("header", false)
        //.option("inferSchema", true)
        .schema(builder)
        .load("src/main/java/resources/test.csv"); //TODO: CMD line arg
        return df;
}

现在可以像下面这样调用了。

    CsvReader cr = new CsvReader(schema);
    Dataset df = cr.getDataframe();
    cr.printSchema();

我建议您重新设计 class。一种选择是您可以将 df 作为参数传递给其他方法。如果您使用的是 Spark 2.0，则不需要 SparkConf。请参考documentation创建SparkSession。

Apache Spark 数据集 API - 不接受架构 StructType

Apache Spark Dataset API - Does not accept schema StructType

java

csv

apache-spark

spark-dataframe

databricks