added takeSamples method

takeSamples method takes a specified number of samples from the RDD and
outputs it in an array.

core/src/main/scala/spark/RDD.scala

@@ -91,6 +91,39 @@ abstract class RDD[T: ClassManifest](@transient sc: SparkContext) extends Serial
   def sample(withReplacement: Boolean, fraction: Double, seed: Int): RDD[T] =
     new SampledRDD(this, withReplacement, fraction, seed)
 
+  def takeSample(withReplacement: Boolean, num: Int, seed: Int): Array[T] = {
+  	var fraction = 0.0
+  	var total = 0
+  	var multiplier = 3.0
+	
+  	if (num > count()) {
+  		total = Math.min(count().toInt)
+  		fraction = 1.0
+  	}
+  	else if (num < 0) {
+  		throw(new IllegalArgumentException())
+  	}
+  	else {
+  		fraction = Math.min(multiplier*(num+1)/count(), 1.0)
+  		total = num.toInt
+  	}
+	
+  	var r = new SampledRDD(this, withReplacement, fraction, seed)
+	
+  	while (r.count() < total) {
+  		r = new SampledRDD(this, withReplacement, fraction, seed)
+  	}
+	
+  	var samples = r.collect()
+  	var arr = new Array[T](total)
+	
+  	for (i <- 0 to total - 1) {
+  		arr(i) = samples(i)
+  	}
+	
+  	return arr
+  }
+
   def union(other: RDD[T]): RDD[T] = new UnionRDD(sc, Array(this, other))
 
   def ++(other: RDD[T]): RDD[T] = this.union(other)