Haskell + division

Question

Im able to sum the zth element of all of the tuples but for some weird reason I only get 1 after dividing my result by 2.

averageYear :: [(String, String, Int)] -> Int
averageYear [] = 0
averageYear ((x,y,z):xs) = (z + (averageYear xs)) `div` (length xs)

Thanks!!

score 6 · Answer 1 · answered Jan 12 '16 at 02:17

6

The math is completely wrong.

averageYear [(_, _, 2010)] = (2010 + averageYear []) `div` 2
                           = (2010 + 0) `div` 2
                           = 2010 `div` 2
                           = 1005

To compute the average, you have to divide the sum by the number of items.

average :: [Int] -> Int
average xs = sum xs `div` length xs

averageYear :: [(String, String, Int)] -> Int
averageYear = average . map (\(_, _, year) -> year)

answered Jan 12 '16 at 02:17

Dietrich Epp

205,541
37
345
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great solution.. could you clarify what the full stop does ( . ) and what the slash does in the last line? ty – ajanakos Jan 12 '16 at 07:19
In Haskell, `(.)` is the function composition operator, and `\x -> y` is a lambda expression. – Dietrich Epp Jan 12 '16 at 07:29

score 0 · Answer 2 · answered Jan 14 '16 at 00:07

0

@Dietrich Epp Length xs is zero and not two in your example.

   averageYear ((x,y,z):xs) = (z + (averageYear xs)) `div` (length xs)

If xs is empty then length xs equal zero and you divide by zero.

answered Jan 14 '16 at 00:07

Zacharie 007

126
4

Haskell + division

2 Answers2