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Aggregate function with key in spark
2022-07-06 21:43:00 【Big data Xiaochen】
RDD Every element of is 【 Key value pair 】 To call the following functions .
groupByKey
aggregateByKey
rdd = sc.parallelize([('a', 1), ('b', 1), ('a', 1), ('b', 1), ('a', 1)], 2)
When aggregating in the following partition , The initial value will participate in the calculation , When aggregating between partitions , The initial value will not participate in the calculation .
foldByKey
foldByKey By aggregateByKey Simplify
When aggregateByKey The logic of aggregation functions within and between partitions of is the same , It can be omitted as a , It becomes foldByKey.
reduceByKey
reduceByKey By foldByKey Simplify
When foldByKey When the initial value of is meaningless , You can omit it
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