1. 從集合創建RDD
def parallelize[T](seq: Seq[T], numSlices: Int = defaultParallelism)(implicit arg0: ClassTag[T]): RDD[T]
目的：從一個Seq集合創建RDD
參數1：Seq集合，必須
參數2：分區數，默認爲該Application分配到的資源的CPU核數
scala> var rdd = sc.parallelize(1 to 10)
rdd: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[2] at parallelize at :21
scala> rdd.collect
res3: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
scala> rdd.partitions.size
res4: Int = 15
//設置RDD爲3個分區
scala> var rdd2 = sc.parallelize(1 to 10,3)
rdd2: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[3] at parallelize at :21
scala> rdd2.collect
res5: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
scala> rdd2.partitions.size
res6: Int = 3
def makeRDD[T](seq: Seq[T], numSlices: Int = defaultParallelism)(implicit arg0: ClassTag[T]): RDD[T]
// 這種用法和parallelize完全相同
def makeRDD[T](seq: Seq[(T, Seq[String])])(implicit arg0: ClassTag[T]): RDD[T]
// 該用法可以指定每一個分區的preferred Locations
scala> var collect = Seq((1 to 10,Seq("slave007.lxw1234.com","slave002.lxw1234.com")),
(11 to 15,Seq("slave013.lxw1234.com","slave015.lxw1234.com")))
collect: Seq[(scala.collection.immutable.Range.Inclusive, Seq[String])] = List((Range(1, 2, 3, 4, 5, 6, 7, 8, 9, 10),
List(slave007.lxw1234.com, slave002.lxw1234.com)), (Range(11, 12, 13, 14, 15),List(slave013.lxw1234.com, slave015.lxw1234.com)))
scala> var rdd = sc.makeRDD(collect)
rdd: org.apache.spark.rdd.RDD[scala.collection.immutable.Range.Inclusive] = ParallelCollectionRDD[6] at makeRDD at :23
scala> rdd.partitions.size
res33: Int = 2
scala> rdd.preferredLocations(rdd.partitions(0))
res34: Seq[String] = List(slave007.lxw1234.com, slave002.lxw1234.com)
scala> rdd.preferredLocations(rdd.partitions(1))
res35: Seq[String] = List(slave013.lxw1234.com, slave015.lxw1234.com)
2. 從外部存儲創建RDD
//從hdfs文件創建
scala> var rdd = sc.textFile("hdfs:///tmp/lxw1234/1.txt")
rdd: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[26] at textFile at :21
scala> rdd.count
res48: Long = 4
//從本地文件創建
scala> var rdd = sc.textFile("file:///etc/hadoop/conf/core-site.xml")
rdd: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[28] at textFile at :21
scala> rdd.count
res49: Long = 97
