Spark kmeans example里有一句scala代码看不懂？

https://github.com/apache/spark/blob/master/examples/src/main/scala/org/apache/spark/examples/SparkKMeans.scala#L82

就是这里第82行

 val pointStats = closest.reduceByKey{case ((p1, c1), (p2, c2)) => (p1 + p2, c1 + c2)}

整个不懂啥意思，
另外，为什么reduceByKey后面是大括号{}

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http://blog.csdn.net/guotong1988/article/details/50834364

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因为后面是一个要处理的语句块呀