我无法理解在使用scala的spark中第一个例子中的reduceByKey(_ + _)。
object WordCount {
def main(args: Array[String]): Unit = {
val inputPath = args(0)
val outputPath = args(1)
val sc = new SparkContext()
val lines = sc.textFile(inputPath)
val wordCounts = lines.flatMap {line => line.split(" ")}
.map(word => (word, 1))
.reduceByKey(_ + _) **I cant't understand this line**
wordCounts.saveAsTextFile(outputPath)
}
}