Spark—将列从RDD或数据帧映射到JAVA中的变量
我试图将Spark RDD中的cassandra行列映射到可以在Spark中进行交互操作的变量,但似乎无法将它们转换为变量。我有以下代码:Spark—将列从RDD或数据帧映射到JAVA中的变量,java,apache-spark,cassandra,datastax-java-driver,Java,Apache Spark,Cassandra,Datastax Java Driver,我试图将Spark RDD中的cassandra行列映射到可以在Spark中进行交互操作的变量,但似乎无法将它们转换为变量。我有以下代码: JavaRDD<MeasuredValue> rdd = javaFunctions(sc).cassandraTable("model", "reports", mapRowTo (MeasuredValue.class)) .select("start_frequency","bandwidth", "power"); Ja
JavaRDD<MeasuredValue> rdd = javaFunctions(sc).cassandraTable("model", "reports", mapRowTo (MeasuredValue.class))
.select("start_frequency","bandwidth", "power");
JavaRDD<Value> valueRdd = rdd.flatMap(row-> {
double start_frequency = row.getStartFrequency();
float power = row.getPower();
double bandwidth = row.getBandwidth();
List<Value> list = new ArrayList<Value>();
// Create Channel Power Buckets
for(channel = 1.6000E8; channel <= channel_end; ){
if( (channel >= start_frequency) && (channel <= (start_frequency + bandwidth)) ) {
list.add(new Value(channel, power));
} // end if
channel+=increment;
} // end for
})
我尝试使用lambda平面映射行的尝试似乎是错误的,因为我得到了以下错误:
无法应用类AbstractJavaRDDLike中的方法flatMap
对给定的类型;必需:找到FlatMapFunction:
(行)->{d[…];}}原因:无法推断类型变量U(参数
不匹配;lambda表达式中的返回类型错误(缺少返回值)
我在“创建通道功率桶”循环中遇到错误
“从lambda表达式引用的局部变量必须是final
或实际上是最终的”
如果我可以用一个数据帧来做这件事,我会有兴趣看到代码来促进这一点。发现答案是:
JavaRDD<MeasuredValue> rdd = javaFunctions(sc).cassandraTable("SB1000_47130646", "Measured_Value", mapRowTo(MeasuredValue.class));
JavaRDD<Value> valueRdd = rdd.flatMap(new FlatMapFunction<MeasuredValue, Value>(){
@Override
public Iterable<Value> call(MeasuredValue row) throws Exception {
double start_frequency = row.getStart_frequency();
float power = row.getPower();
double bandwidth = row.getBandwidth();
// Define Variable
double channel,channel_end, increment;
// Initialize Variables
channel_end = 1.6159E8;
increment = 5000;
List<Value> list = new ArrayList<Value>();
// Create Channel Power Buckets
for(channel = 1.6000E8; channel <= channel_end; ){
if( (channel >= start_frequency) && (channel <= (start_frequency + bandwidth)) ) {
list.add(new Value(channel, power));
} // end if
channel+=increment;
} // end for
return list;
}
});
sqlContext.createDataFrame(valueRdd, Value.class).groupBy(col("channel"))
.agg(min("power"), max("power"), avg("power"))
.write().mode(SaveMode.Append)
.option("table", "results")
.option("keyspace", "model")
.format("org.apache.spark.sql.cassandra").save();
} // end session
} // End Compute
public class Value implements Serializable {
public Value(Double channel, Float power) {
this.channel = channel;
this.power = power;
}
Double channel;
Float power;
public void setChannel(Double channel) {
this.channel = channel;
}
public void setPower(Float power) {
this.power = power;
}
public Double getChannel() {
return channel;
}
public Float getPower() {
return power;
}
@Override
public String toString() {
return "[" +channel +","+power+"]";
}
}
public static class MeasuredValue implements Serializable {
public MeasuredValue() { }
private double start_frequency;
public double getStart_frequency() { return start_frequency; }
public void setStart_frequency(double start_frequency) { this.start_frequency = start_frequency; }
private double bandwidth ;
public double getBandwidth() { return bandwidth; }
public void setBandwidth(double bandwidth) { this.bandwidth = bandwidth; }
private float power;
public float getPower() { return power; }
public void setPower(float power) { this.power = power; }
}
JavaRDD rdd=javaFunctions(sc).cassandraTable(“SB1000_47130646”,“测量值”,mapRowTo(MeasuredValue.class));
JavaRDD valueRdd=rdd.flatMap(新的flatMap函数(){
@凌驾
公共Iterable调用(MeasuredValue行)引发异常{
双启动_频率=行。getStart_频率();
float power=row.getPower();
double带宽=row.getBandwidth();
//定义变量
双通道,通道末端,增量;
//初始化变量
通道_端=1.6159E8;
增量=5000;
列表=新的ArrayList();
//创建通道功率桶
对于(通道=1.6000E8;通道=启动频率)和(通道我应该使用数据帧而不是RDD吗?第二条错误消息表明lambda中使用的一些变量没有声明为final-什么是increment
和channel\u end
变量?它们是final
?它们的定义如下://定义变量双通道,channel\u end,start\fr频率,增量,带宽;浮点功率;长时间\u键;//初始化变量通道\u端=1.6159E8;增量=5000;
那么就这样了(或部分)-它们必须是最终的,例如,final double channel_end=1.6159E8;
主要问题是能够将行-列值映射到变量。我可以从spark内部进行操作。
JavaRDD<MeasuredValue> rdd = javaFunctions(sc).cassandraTable("SB1000_47130646", "Measured_Value", mapRowTo(MeasuredValue.class));
JavaRDD<Value> valueRdd = rdd.flatMap(new FlatMapFunction<MeasuredValue, Value>(){
@Override
public Iterable<Value> call(MeasuredValue row) throws Exception {
double start_frequency = row.getStart_frequency();
float power = row.getPower();
double bandwidth = row.getBandwidth();
// Define Variable
double channel,channel_end, increment;
// Initialize Variables
channel_end = 1.6159E8;
increment = 5000;
List<Value> list = new ArrayList<Value>();
// Create Channel Power Buckets
for(channel = 1.6000E8; channel <= channel_end; ){
if( (channel >= start_frequency) && (channel <= (start_frequency + bandwidth)) ) {
list.add(new Value(channel, power));
} // end if
channel+=increment;
} // end for
return list;
}
});
sqlContext.createDataFrame(valueRdd, Value.class).groupBy(col("channel"))
.agg(min("power"), max("power"), avg("power"))
.write().mode(SaveMode.Append)
.option("table", "results")
.option("keyspace", "model")
.format("org.apache.spark.sql.cassandra").save();
} // end session
} // End Compute
public class Value implements Serializable {
public Value(Double channel, Float power) {
this.channel = channel;
this.power = power;
}
Double channel;
Float power;
public void setChannel(Double channel) {
this.channel = channel;
}
public void setPower(Float power) {
this.power = power;
}
public Double getChannel() {
return channel;
}
public Float getPower() {
return power;
}
@Override
public String toString() {
return "[" +channel +","+power+"]";
}
}
public static class MeasuredValue implements Serializable {
public MeasuredValue() { }
private double start_frequency;
public double getStart_frequency() { return start_frequency; }
public void setStart_frequency(double start_frequency) { this.start_frequency = start_frequency; }
private double bandwidth ;
public double getBandwidth() { return bandwidth; }
public void setBandwidth(double bandwidth) { this.bandwidth = bandwidth; }
private float power;
public float getPower() { return power; }
public void setPower(float power) { this.power = power; }
}