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|
module Utils.List exposing
( groupBy
, mean
, links
)
import Dict
import Maybe.Extra as Maybe
groupBy : (a -> comparable) -> List a -> List (comparable, List a)
groupBy f xs =
let addItem item dict =
let groupItems = Dict.get (f item) dict |> Maybe.withDefault []
in Dict.insert (f item) (item :: groupItems) dict
in List.foldr addItem Dict.empty xs
|> Dict.toList
mean : List Int -> Int
mean xs = (List.sum xs) // (List.length xs)
links : List a -> List (a, a)
links xs =
let reversed = List.reverse xs
in List.foldr
(\x acc ->
case Maybe.map Tuple.first (List.head acc) of
Just y ->
(x, y) :: acc
_ ->
acc
)
(case reversed of
x :: y :: _ -> [(y, x)]
_ -> []
)
(List.reverse << List.drop 2 <| reversed)
|
