Haskell +师

Question

我能够将所有元组的第z个元素相加,但由于一些奇怪的原因,我将结果除以2后得到1.

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

谢谢!!

Answer 1

数学是完全错误的.

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

要计算平均值,您必须将总和除以项目数.

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

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