使用数据数组我如何在转换为华氏温度后输出数据数组。 - Haskell

Question

我想从 cities 数组中的所有数据中获取温度并以华氏度输出数据。

我尝试过的所有方法似乎都不起作用，正如您所见，getAllTempsF 是我最近的尝试。

C 到 F 是 (c*1.8)+18

data City = City { cityName :: String
                        , temperature :: [Double] 
                        }

city1 = City {cityName = "city1", temperature = [4.50,6.50,5.0,6.48,8.54]}
city2 = City {cityName = "city2", temperature = [6.35,5.12,3.21,3.25,4.56]}
city3 = City {cityName = "city3", temperature = [7.3,5.32,4.4,4.6]}

cities :: [City]
cities = [city1,city2,city3]

getAllNames :: [City] -> [String]
getAllNames x = map cityName x

getAllTemps :: [City] -> [[Double]]
getAllTemps x = map temperature x

getAllTempsF :: [City] -> [[Double]]
getAllTempsF [] = 1
getAllTempsF (x:xs) = [((x * 1.8) + 32)..] >>  getAllTempsF xs

Answer 1

您已经在getAllTemps中使用了map，意思是“对列表的每个元素做一些事情”。 getAllTempsF 也可以表述为“对列表的每个元素做某事”，在这种情况下，“某事”是一些数学。唯一的区别是我们处理的是列表的列表，而不是单个列表。我们仍然可以使用map来写这个函数；我们只需要做两次。

getAllTempsF :: [City] -> [[Double]]
getAllTempsF xs = map (map (\x -> x * 1.8 + 32)) $ getAllTemps xs

现在我们在列表列表中有了它。您提到打印出数据，为此我们将使用 forM_，它与 map 类似，但用于副作用而不是值。

printOutTemps :: [City] -> IO ()
printOutTemps cities = do
  -- Get each city, together with its temperatures in a list.
  let cityData = zip cities (getAllTempsF cities)
  -- For each one... do some IO.
  forM_ cityData $ \(city, tempsF) -> do
    -- Get the temperatures as a list of strings, so we can print them out.
    let tempsStr = map show tempsF
    -- Print out the city names and the temperatures.
    putStrLn $ (cityName city) ++ " has temperatures " ++ unwords tempsStr

Try it online!

如果您还没有找到此特定资源，Hoogle is a great site for identifying Haskell functions. So if you don't know what any of the functions I used in this answer do, you can always search them on Hoogle. For instance, if you don't know what zip does, you can search zip 第一个结果正是您要查找的函数。

使用数据数组我如何在转换为华氏温度后输出数据数组。 - Haskell

Using data arrays how do i ouput arrays of data after converting to fahrenheit. - Haskell

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