A minimal definition of a columnar dataframe with a closed.

DataFrame.hs

module DataFrame where

-- Column space with a closed type universe.
data Column = CInt [Int]
            | CDouble [Double]
            | CString [String]

instance Show Column where
    show (CInt xs) = show xs
    show (CDouble xs) = show xs
    show (CString xs) = show xs

class ToColumn a where
  fromList :: [a] -> Column

instance ToColumn Int    where fromList = CInt
instance ToColumn Double where fromList = CDouble
instance ToColumn String where fromList = CString

class Transform a b where
  transform :: (a -> b) -> Column -> Column

instance Transform Int Int where
    transform f (CInt xs) = fromList (map f xs)

instance Transform Int Double where
    transform f (CInt xs) = fromList (map f xs)

instance Transform Int String where
    transform f (CInt xs) = fromList (map f xs)

instance Transform Double Int where
    transform f (CDouble xs) = fromList (map f xs)

instance Transform Double Double where
    transform f (CDouble xs) = fromList (map f xs)

instance Transform Double String where
    transform f (CDouble xs) = fromList (map f xs)

instance Transform String Int where
    transform f (CString xs) = fromList (map f xs)

instance Transform String Double where
    transform f (CString xs) = fromList (map f xs)

instance Transform String String where
    transform f (CString xs) = fromList (map f xs)

data DataFrame = DataFrame {
    columns :: [(String, Column)]
} deriving (Show)

fromNamedColumns :: [(String, Column)] -> DataFrame
fromNamedColumns = DataFrame