CODEWITHSUNDEEP
scalascala-collections
user9715375
user9715375

Reputation: 61

Error in reduceLeft in Map?

I'm trying to add key, value pairs in a Map using reduceLeft() but am getting a error. If I add the key value pair using foldleft() I get the right answer. What does this Error mean in reduceLeft and what is the correct code?

Code:

object Dcoder extends App
{
    var i = Map(1->2, 3->4, 5->6)
    var o = i.reduceLeft((a,b) => a._1 + b._1)
    println(o)
}

Error:

source_file.scala:9: error: type mismatch;
 found   : Int
 required: (Int, Int)
var o=i.reduceLeft((a,b)=>a._1+b._1)
                          ^
one error found

Upvotes: 1

Views: 200

Answers (1)

jwvh
jwvh

Reputation: 51271

You can fold from one type to another but reduce is more restrictive. You can't reduce a collection of pairs, type (Int,Int), to a single type Int.

This works by reducing a collection of pairs to a singe pair and then stripping away the 2nd element.

Map(1->2, 3->4, 5->6).reduceLeft(_._1 + _._1 -> 0)._1  //res0: Int = 9

Upvotes: 2

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