Agrupamiento según valores

3 Comentarios

1. Haskell

   agrupa :: Ord c => (a -> c) -> [a] -> M.Map c [a] agrupa f = foldr (\x -> M.insertWith (++) (f x) [x]) M.empty

   1 2	agrupa :: Ord c => (a -> c) -> [a] -> M.Map c [a] agrupa f = foldr (\x -> M.insertWith (++) (f x) [x]) M.empty

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2. Haskell

   agrupa :: Ord c => (a -> c) -> [a] -> Map c [a] agrupa f xs = fromListWith (++) [(f x, [x]) | x <- xs]

   1 2	agrupa :: Ord c => (a -> c) -> [a] -> Map c [a] agrupa f xs = fromListWith (++) [(f x, [x]) | x <- xs]

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   1. Es extraño, pero fromListWith me cambia el orden de los valores del mapa.

      ghci> agrupa length ["hoy", "ayer", "ana", "cosa"] fromList [(3,["ana","hoy"]),(4,["cosa","ayer"])]

      1 2	ghci> agrupa length ["hoy", "ayer", "ana", "cosa"] fromList [(3,["ana","hoy"]),(4,["cosa","ayer"])]

      Para ajustarse a los ejemplos, es necesario invertir la lista:

      Haskell

      agrupa :: Ord c => (a -> c) -> [a] -> Map c [a] agrupa f xs = fromListWith (++) [(f x, [x]) | x <- reverse xs]

      1 2	agrupa :: Ord c => (a -> c) -> [a] -> Map c [a] agrupa f xs = fromListWith (++) [(f x, [x]) | x <- reverse xs]

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