Spark修煉之道（進階篇）——Spark入門到精通：第五節 Spark程式設計模型（二)

本文主要內容

1. RDD 常用Transformation函式

1. RDD 常用Transformation函式

（1）union 
union將兩個RDD資料集元素合併，類似兩個集合的並集 
union函式引數：

<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與另外一個RDD進行Union操作之後，兩個資料集中的存在的重複元素 
程式碼如下：

<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>
//存在重複元素
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>

（2）intersection 
方法返回兩個RDD資料集的交集 
函式引數： 
/** 
* 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函式將去除重複元素 
distinct函式引數：

/** 
* 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>

（4）groupByKey([numTasks]) 
輸入資料為(K, V) 對, 返回的是 (K, Iterable) ，numTasks指定task數量，該引數是可選的，下面給出的是無引數的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函式輸入資料為(K, V)對，返回的資料集結果也是（K,V）對，只不過V為經過聚合操作後的值 
/** 
* 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>

（6）sortByKey([ascending], [numTasks]) 
對輸入的資料集按key排序 
sortByKey方法定義

<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>

（7）join(otherDataset, [numTasks]) 
對於資料集型別為 (K, V) 及 (K, W)的RDD，join操作後返回型別為 (K, (V, W))，join函式有三種： 
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>

<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>

<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>

（8）cogroup(otherDataset, [numTasks]) 
如果輸入的RDD型別為(K, V) 和(K, W)，則返回的RDD型別為 (K, (Iterable, Iterable)) . 該操作與 groupWith等同

方法定義： 
/** 
* 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>

（9）cartesian(otherDataset) 
求兩個RDD資料集間的笛卡爾積 
函式定義： 
/** 
* 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>

（10）coalesce(numPartitions) 
將RDD的分割槽數減至指定的numPartitions分割槽數

函式定義： 
/** 
* 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]

示例程式碼：

<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>

repartition(numPartitions)，功能與coalesce函式相同，實質上它呼叫的就是coalesce函式，只不是shuffle = true，意味著可能會導致大量的網路開銷。 
方法定義： 
/** 
* 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) 

}

轉載： http://blog.csdn.net/lovehuangjiaju/article/details/48603009