Spark修炼之道（进阶篇）——Spark入门到精通：第五节 Spark编程模型（二)

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本文深入探讨了大数据开发领域中关键组件的应用与实战经验，包括Hadoop、Spark、Flink等主流技术的使用场景与优化策略，旨在帮助开发者高效解决数据处理与分析难题。

本文主要内容

RDD 常用Transformation函数

1. RDD 常用Transformation函数

（1）union
union将两个RDD数据集元素合并，类似两个集合的并集
union函数参数：

<code class="hljs python has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> /**
   * Return the union of this RDD <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span> another one. Any identical elements will appear multiple
   * times (use `.distinct()` to eliminate them).
   */
  <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">def</span> <span class="hljs-title" style="box-sizing: border-box;">union</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(other: RDD[T])</span>:</span> RDD[T] </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

RDD与另外一个RDD进行Union操作之后，两个数据集中的存在的重复元素
代码如下：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">scala> val rdd1=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> to <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>)
<span class="hljs-label" style="box-sizing: border-box;">rdd1:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[Int] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">15</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> val rdd2=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span> to <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>)
<span class="hljs-label" style="box-sizing: border-box;">rdd2:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[Int] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">16</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>
//存在重复元素
scala> rdd1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.union</span>(rdd2)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.collect</span>
<span class="hljs-label" style="box-sizing: border-box;">res13:</span> Array[Int] = Array(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>)
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

这里写图片描述

（2）intersection
方法返回两个RDD数据集的交集
函数参数：
/**
* Return the intersection of this RDD and another one. The output will not contain any duplicate
* elements, even if the input RDDs did.
*
* Note that this method performs a shuffle internally.
*/
def intersection(other: RDD[T]): RDD[T]

使用示例：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">scala> rdd1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.intersection</span>(rdd2)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.collect</span>
<span class="hljs-label" style="box-sizing: border-box;">res14:</span> Array[Int] = Array(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>)
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

（3）distinct
distinct函数将去除重复元素
distinct函数参数：

/**
* Return a new RDD containing the distinct elements in this RDD.
*/
def distinct(): RDD[T]

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">scala> val rdd1=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> to <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>)
<span class="hljs-label" style="box-sizing: border-box;">rdd1:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[Int] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> val rdd2=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span> to <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>)
<span class="hljs-label" style="box-sizing: border-box;">rdd2:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[Int] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> rdd1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.union</span>(rdd2)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.distinct</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.collect</span>
<span class="hljs-label" style="box-sizing: border-box;">res0:</span> Array[Int] = Array(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>)
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

这里写图片描述

（4）groupByKey([numTasks])
输入数据为(K, V) 对, 返回的是 (K, Iterable) ，numTasks指定task数量，该参数是可选的，下面给出的是无参数的groupByKey方法
/**
* Group the values for each key in the RDD into a single sequence. Hash-partitions the
* resulting RDD with the existing partitioner/parallelism level. The ordering of elements
* within each group is not guaranteed, and may even differ each time the resulting RDD is
* evaluated.
*
* Note: This operation may be very expensive. If you are grouping in order to perform an
* aggregation (such as a sum or average) over each key, using [[PairRDDFunctions.aggregateByKey]]
* or [[PairRDDFunctions.reduceByKey]] will provide much better performance.
*/
def groupByKey(): RDD[(K, Iterable[V])]

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">scala> val rdd1=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> to <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>)
<span class="hljs-label" style="box-sizing: border-box;">rdd1:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[Int] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> val rdd2=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span> to <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>)
<span class="hljs-label" style="box-sizing: border-box;">rdd2:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[Int] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> rdd1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.union</span>(rdd2)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.map</span>((_,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>))<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.groupByKey</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.collect</span>
<span class="hljs-label" style="box-sizing: border-box;">res2:</span> Array[(Int, Iterable[Int])] = Array((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>,CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>,CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>,CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>,CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>,CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>,CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)))
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

（5）reduceByKey(func, [numTasks])
reduceByKey函数输入数据为(K, V)对，返回的数据集结果也是（K,V）对，只不过V为经过聚合操作后的值
/**
* Merge the values for each key using an associative reduce function. This will also perform
* the merging locally on each mapper before sending results to a reducer, similarly to a
* “combiner” in MapReduce. Output will be hash-partitioned with numPartitions partitions.
*/
def reduceByKey(func: (V, V) => V, numPartitions: Int): RDD[(K, V)]

使用示例：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">scala> rdd1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.union</span>(rdd2)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.map</span>((_,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>))<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.reduceByKey</span>(_+_)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.collect</span>
<span class="hljs-label" style="box-sizing: border-box;">res4:</span> Array[(Int, Int)] = Array((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>))</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>

这里写图片描述

（6）sortByKey([ascending], [numTasks])
对输入的数据集按key排序
sortByKey方法定义

<code class="hljs coffeescript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">/**
   * Sort the RDD <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">by</span> key, so that each partition contains a sorted range <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> the elements. Calling
   * `<span class="javascript" style="box-sizing: border-box;">collect</span>` <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">or</span> `<span class="javascript" style="box-sizing: border-box;">save</span>` <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">on</span> the resulting RDD will <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">or</span> output an ordered list <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> records
   * (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> the `<span class="javascript" style="box-sizing: border-box;">save</span>` <span class="hljs-reserved" style="box-sizing: border-box;">case</span>, they will be written to multiple `<span class="javascript" style="box-sizing: border-box;">part-X</span>` files <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> the filesystem, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span>
   * order <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> the keys).
   */
  <span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(0, 136, 0);">TODO</span>: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span> currently doesn<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'t work on P other than Tuple2!
  def sortByKey(ascending: Boolean = true, numPartitions: Int = self.partitions.length)
      : RDD[(K, V)]</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

使用示例：

<code class="hljs haskell has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-title" style="box-sizing: border-box;">scala</span>> var <span class="hljs-typedef" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">data</span> = sc.parallelize<span class="hljs-container" style="box-sizing: border-box;">(<span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">List</span>((1,3)</span>,<span class="hljs-container" style="box-sizing: border-box;">(1,2)</span>,<span class="hljs-container" style="box-sizing: border-box;">(1, 4)</span>,<span class="hljs-container" style="box-sizing: border-box;">(2,3)</span>,<span class="hljs-container" style="box-sizing: border-box;">(7,9)</span>,<span class="hljs-container" style="box-sizing: border-box;">(2,4)</span>))</span>
<span class="hljs-typedef" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">data</span>: org.apache.spark.rdd.<span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">RDD</span>[<span class="hljs-container" style="box-sizing: border-box;">(<span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">Int</span>, <span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">Int</span>)</span>] = <span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">ParallelCollectionRDD</span>[20] at parallelize at <console>:21</span>

<span class="hljs-title" style="box-sizing: border-box;">scala</span>> <span class="hljs-typedef" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">data</span>.sortByKey<span class="hljs-container" style="box-sizing: border-box;">(<span class="hljs-title" style="box-sizing: border-box;">true</span>)</span>.collect</span>
<span class="hljs-title" style="box-sizing: border-box;">res10</span>: <span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">Array</span>[(<span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">Int</span>, <span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">Int</span>)] = <span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">Array</span>((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">9</span>))

</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

这里写图片描述

（7）join(otherDataset, [numTasks])
对于数据集类型为 (K, V) 及 (K, W)的RDD，join操作后返回类型为 (K, (V, W))，join函数有三种：
def join[W](other: RDD[(K, W)], partitioner: Partitioner): RDD[(K, (V, W))]
def leftOuterJoin[W](
other: RDD[(K, W)],
partitioner: Partitioner): RDD[(K, (V, Option[W]))]
def rightOuterJoin[W](other: RDD[(K, W)], partitioner: Partitioner)
: RDD[(K, (Option[V], W))]

使用示例：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">scala> val rdd1=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(Array((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>),(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>))
     | )
<span class="hljs-label" style="box-sizing: border-box;">rdd1:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[(Int, Int)] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">24</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> val rdd2=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(Array((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>)))
<span class="hljs-label" style="box-sizing: border-box;">rdd2:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[(Int, Int)] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">32</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> rdd1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.join</span>(rdd2)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.collect</span>
<span class="hljs-label" style="box-sizing: border-box;">res13:</span> Array[(Int, (Int, Int))] = Array((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>)), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>)))
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

这里写图片描述

<code class="hljs vbscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">scala> rdd1.leftOuterJoin(rdd2).collect
res15: <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Array</span>[(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Int</span>, (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Int</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Option</span>[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Int</span>]))] = <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Array</span>((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>,Some(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>))), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,Some(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>))))</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>

这里写图片描述

<code class="hljs vbscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">scala> rdd1.rightOuterJoin(rdd2).collect
res16: <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Array</span>[(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Int</span>, (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Option</span>[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Int</span>], <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Int</span>))] = <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Array</span>((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,(Some(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>),<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>)), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,(Some(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>),<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>)))
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

这里写图片描述

（8）cogroup(otherDataset, [numTasks])
如果输入的RDD类型为(K, V) 和(K, W)，则返回的RDD类型为 (K, (Iterable, Iterable)) . 该操作与 groupWith等同

方法定义：
/**
* For each key k in this or other, return a resulting RDD that contains a tuple with the
* list of values for that key in this as well as other.
*/
def cogroup[W](other: RDD[(K, W)], partitioner: Partitioner)
: RDD[(K, (Iterable[V], Iterable[W]))]

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">scala> val rdd1=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(Array((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>),(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>))
     | )
<span class="hljs-label" style="box-sizing: border-box;">rdd1:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[(Int, Int)] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">24</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> val rdd2=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(Array((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>)))
<span class="hljs-label" style="box-sizing: border-box;">rdd2:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[(Int, Int)] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">32</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> rdd1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.cogroup</span>(rdd2)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.collect</span>
<span class="hljs-label" style="box-sizing: border-box;">res17:</span> Array[(Int, (Iterable[Int], Iterable[Int]))] = Array((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,(CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>),CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>))))

scala> rdd1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.groupWith</span>(rdd2)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.collect</span>
<span class="hljs-label" style="box-sizing: border-box;">res18:</span> Array[(Int, (Iterable[Int], Iterable[Int]))] = Array((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,(CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>),CompactBuffer(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>))))
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>

这里写图片描述

（9）cartesian(otherDataset)
求两个RDD数据集间的笛卡尔积
函数定义：
/**
* Return the Cartesian product of this RDD and another one, that is, the RDD of all pairs of
* elements (a, b) where a is in this and b is in other.
*/
def cartesian[U: ClassTag](other: RDD[U]): RDD[(T, U)]

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">scala> val rdd1=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(Array(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>))
<span class="hljs-label" style="box-sizing: border-box;">rdd1:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[Int] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">52</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> val rdd2=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(Array(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>))
<span class="hljs-label" style="box-sizing: border-box;">rdd2:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[Int] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">53</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> rdd1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.cartesian</span>(rdd2)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.collect</span>
<span class="hljs-label" style="box-sizing: border-box;">res21:</span> Array[(Int, Int)] = Array((<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>), (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>))
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

这里写图片描述

（10）coalesce(numPartitions)
将RDD的分区数减至指定的numPartitions分区数

函数定义：
/**
* Return a new RDD that is reduced into numPartitions partitions.
*
* This results in a narrow dependency, e.g. if you go from 1000 partitions
* to 100 partitions, there will not be a shuffle, instead each of the 100
* new partitions will claim 10 of the current partitions.
*
* However, if you’re doing a drastic coalesce, e.g. to numPartitions = 1,
* this may result in your computation taking place on fewer nodes than
* you like (e.g. one node in the case of numPartitions = 1). To avoid this,
* you can pass shuffle = true. This will add a shuffle step, but means the
* current upstream partitions will be executed in parallel (per whatever
* the current partitioning is).
*
* Note: With shuffle = true, you can actually coalesce to a larger number
* of partitions. This is useful if you have a small number of partitions,
* say 100, potentially with a few partitions being abnormally large. Calling
* coalesce(1000, shuffle = true) will result in 1000 partitions with the
* data distributed using a hash partitioner.
*/
def coalesce(numPartitions: Int, shuffle: Boolean = false)(implicit ord: Ordering[T] = null)
: RDD[T]

示例代码：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">scala> val rdd1=sc<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.parallelize</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> to <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>)
<span class="hljs-label" style="box-sizing: border-box;">rdd1:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[Int] = ParallelCollectionRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">55</span>] at parallelize at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span>

scala> val rdd2=rdd1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.coalesce</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>)
<span class="hljs-label" style="box-sizing: border-box;">rdd2:</span> org<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.apache</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.spark</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.rdd</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.RDD</span>[Int] = CoalescedRDD[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">56</span>] at coalesce at <console>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">23</span>
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

这里写图片描述

repartition(numPartitions)，功能与coalesce函数相同，实质上它调用的就是coalesce函数，只不是shuffle = true，意味着可能会导致大量的网络开销。
方法定义：
/**
* Return a new RDD that has exactly numPartitions partitions.
*
* Can increase or decrease the level of parallelism in this RDD. Internally, this uses
* a shuffle to redistribute data.
*
* If you are decreasing the number of partitions in this RDD, consider using coalesce,
* which can avoid performing a shuffle.
*/
def repartition(numPartitions: Int)(implicit ord: Ordering[T] = null): RDD[T] = withScope {
coalesce(numPartitions, shuffle = true)

}

转载： http://blog.youkuaiyun.com/lovehuangjiaju/article/details/48603009