CODEWITHSUNDEEP
scala
mop
mop

Reputation: 433

how to use reduce function to add every tuple2's value from every inner List

a List for example:

List(List((0,1), (1,2), (0,0), (1,1)),List((0,1), (1,2), (2,2), (3,3)))

expected:

List((0,2), (2,4), (2,2), (4,4))

how to use reduce function to add every tuple2's value from each inner List

List(List((0,1), (1,2), (0,0), (1,1)),List((0,1), (1,2), (2,2), (3,3))).reduce((a,b)=>a.zip(b))

i don't know how to realize it,so ask for help. thx

Upvotes: 0

Views: 56

Answers (2)

jwvh
jwvh

Reputation: 51271

You're almost there. After the lists have been zipped, map over it so that the resulting list of type List[((Int,Int),(Int,Int))] can be combined to the desired type List[(Int,Int)].

lst.reduce { (x, y) =>
  x zip y map {case ((a,b),(c,d)) => (a+c,b+d)}
}

You might also consider using zipAll() just in case there are internal lists of different lengths.

lst.reduce { (x, y) =>
  x.zipAll(y,(0,0),(0,0)).map{case ((a,b),(c,d)) => (a+c,b+d)}
}

Upvotes: 4

Ramesh Maharjan
Ramesh Maharjan

Reputation: 41957

@jwvh's answer should suffice your problem. But if you would like yet another way to try, then you can try as following too.

val list = List(List((0,1), (1,2), (0,0), (1,1)),List((0,1), (1,2), (2,2), (3,3)))
list.reduce((a,b) => a.zip(b).map(tuple => (tuple._1._1 + tuple._2._1, tuple._1._2 + tuple._2._2)))

Upvotes: 0

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