结合Spark源码分析, combineByKey, aggregateByKey, foldByKey, reduceByKey
转载请标明出处:小帆的帆的专栏combineByKeydefcombineByKey[C](createCombiner:V=>C,mergeValue:(C,V)=>C,mergeCombiners:(C,C)=>C):RDD[(K,C)]=self.withScope{combineByKeyWithClassTag(createCombiner,mergeValue,mergeCombine