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Spark Programming by Java——RDD基本操作

2016-04-15 17:41 489 查看
在一个内容为{1, 2, 3, 3}的RDD上进行的基本操作

函数名(表现形式为scala)目的示例结果
collect()返回RDD中的所有元素rdd.example(){1, 2, 3, 4}
count()RDD中的元素数目rdd.count()4
countByValue()RDD中每个元素的出现次数rdd.countByValue(){(1,1),(2,1),(3,2)}
take(num)返回RDD中num个数量的元素rdd.take(2){1,2}
top(num)返回RDD中最大的num个元素rdd.top(2){3,3}
takeOrdered(num)(ordering)根据你给的排序方法返回一个元素序列rdd.takeOrdered(2)(myOrdering){3, 3}
takeSample(withReplacement, num, [speed])随机返回num个元素rdd.takeSample(false, 1)无值
reduce(func)在一次遍历中合并RDD中所有的元素(例如,求和)rdd.reduce((x, y) => x + y)9
fold(zero)(func)和reduce功能一样,但是提供一个初值rdd.fold(0)((x, y) => x + y)9
aggregate(zeroValue)(seqOp, comOp)和reduce()函数类似,但是用于返回不同的数据类型rdd.aggregate((0, 0)) ((x, y) =>(x._1 + y, x._2 + 1), (x, y) =>(x._1 + y._1, x._2 + y._2))(9,4)
foreach(func)将RDD中所有的元素都用于提供的方法rdd.foreach(func)nothing
Java实现基本代码

import java.util.Arrays;
import java.util.List;

import org.apache.spark.SparkConf;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.JavaSparkContext;
import org.apache.spark.api.java.function.Function2;
import org.apache.spark.api.java.function.VoidFunction;

public class SimpleRDD {
public static void main(String[] args) {
SparkConf conf = new SparkConf().setMaster("local").setAppName("SimpleRDD");
JavaSparkContext sc = new JavaSparkContext(conf);

JavaRDD<Integer> rdd = sc.parallelize(Arrays.asList(1, 2, 3 ,3), 2);

System.out.println("rdd collect" + rdd.collect());
System.out.println("rdd count" + rdd.count());
System.out.println("rdd countByValue" + rdd.countByValue());
System.out.println("rdd take" + rdd.take(2));
System.out.println("rdd top" + rdd.top(2));
System.out.println("rdd takeOrdered" + rdd.takeOrdered(2));
System.out.println("rdd reduce" + rdd.reduce((x, y) -> x + y));
System.out.println("rdd fold" + rdd.fold(0, (x, y) -> x+y));

System.out.println("rdd aggregate test");
List<Integer> data = Arrays.asList(5, 1, 1, 4, 4, 2, 2);
JavaRDD<Integer> javaRDD = sc.parallelize(data, 2);
Integer aggregateValue = javaRDD.aggregate(3, new Function2<Integer, Integer, Integer>() {
@Override
public Integer call(Integer v1, Integer v2) throws Exception {
System.out.println("seq~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" + v1 + "," + v2);
return Math.max(v1, v2);
}
}, new Function2<Integer, Integer, Integer>() {
int i = 0;
@Override
public Integer call(Integer v1, Integer v2) throws Exception {
System.out.println("comb~~~~~~~~~i~~~~~~~~~~~~~~~~~~~"+i++);
System.out.println("comb~~~~~~~~~v1~~~~~~~~~~~~~~~~~~~" + v1);
System.out.println("comb~~~~~~~~~v2~~~~~~~~~~~~~~~~~~~" + v2);
return v1 + v2;
}
});
System.out.println("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"+aggregateValue);

System.out.println("foreach");
rdd.foreach(new VoidFunction<Integer>() {

@Override
public void call(Integer t) throws Exception {
System.out.println(t);

}

});

}
}
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