CODEWITHSUNDEEP
scalafoldleft
Sergey Bushmanov
Sergey Bushmanov

Reputation: 25189

foldLeft on List of Tuples: strange unexpected results

I am having a list of tuples which elements I want to be summed:

val t = Seq(1,2,3,4,5).map(el => (el,1))
t: Seq[(Int, Int)] = List((1,1), (2,1), (3,1), (4,1), (5,1))

t.foldLeft(0,0){ case ((a,b),(c,d)) => (a+b,c+d)}
res3: (Int, Int) = (14,6)

The answer (14,6) is unexpected indeed (expected one was (15,5)).

What puzzles me even more:

t.foldLeft(0,1){ case ((a,b),(c,d)) => (a+b,c+d)}
res3: (Int, Int) = (15,6)

My questions are what do parameters in foldLeft(x,y) correspond to (are they initiation params for 1st and 2nd folds???) and how to get the desired sums over 1st and 2nd elements of tuple.

Upvotes: 1

Views: 247

Answers (1)

Nyavro
Nyavro

Reputation: 8866

You have an error in your folding function. Your accumulator is in (a,b) and element is in (c,d). In order to sum you should return (a+c, b+d)

Upvotes: 7

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