[英]reduceByKey type mismatch
我有這個清單
res22: Array[(String, List[(String, Int)])] = Array((Door_182,List((IN,1), (IN,1))), (Door_89,List((IN,1), (IN,1), (IN,1))), (Door_180,List((IN,1), (IN,1), (IN,1), (IN,1))), (Door_83,List((IN,1), (IN,1), (IN,1))), (Door_177,List((IN,1), (IN,1))), (Door_23,List((IN,1), (IN,1))), (Door_128,List((IN,1), (IN,1))), (Door_34,List((IN,1), (IN,1))), (Door_18,List((IN,1), (IN,1))), (Door_32,List((IN,1))), (Door_76,List((IN,1), (IN,1), (IN,1))), (Door_87,List((IN,1), (IN,1), (IN,1))), (Door_197,List((IN,1), (IN,1))), (Door_133,List((IN,1), (IN,1))), (Door_119,List((IN,1), (IN,1))), (Door_113,List((IN,1), (IN,1), (IN,1), (IN,1), (IN,1))), (Door_155,List((IN,1), (IN,1), (IN,1), (IN,1), (IN,1))), (Door_168,List((IN,1), (IN,1), (IN,1))), (Door_115,List((IN,1), (IN,1))), (Door_9,List((IN,1), (IN,1))),...
我試圖用這個來總結每個門的IN數量:
scala> reduced.map(n => (n._1, n._2)).reduceByKey((v1,v2) => v1 + v2.toString).collect
我收到此錯誤:
<console>:32: error: type mismatch;
found : List[(String, Int)]
required: String
reduced.map(n => (n._1, n._2)).reduceByKey((v1,v2) => v1 + v2).collect
^
我該如何解決?
您可以分兩個步驟進行操作:對於每個鍵,將所有列表匯總在一起,然后對每個列表中的所有值求和:
val x = sc.parallelize(List(("Door_182",List(("IN",1), ("IN",1))), ("Door_89",List(("IN",1), ("IN",1), ("IN",1))), ("Door_180",List(("IN",1), ("IN",1), ("IN",1), ("IN",1))), ("Door_83",List(("IN",1), ("IN",1), ("IN",1))), ("Door_177",List(("IN",1), ("IN",1)))))
x.reduceByKey(_ ::: _)
.map {
case (door, list) => (door, list.foldLeft(0){
case (count1, (in2, count2)) => count1 + count2
})
}.collect()
res3: Array[(String, Int)] = Array((Door_180,4), (Door_83,3), (Door_177,2), (Door_182,2), (Door_89,3))
或在帶有aggregateByKey的單個操作中避免額外的內存分配:
x.aggregateByKey(0)(
{
case (count, list) => count + list.foldLeft(0){
case (count1, (in2, count2)) => count1 + count2}
},
_ +_
)
.collect()
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