Elm: Fold specific values of multiple lists - elm

Question

games =
[ { id = 1
, points =
[ { player_id = 1, score = 20 }
, { player_id = 2, score = 10 }
, { player_id = 3, score = 0 }
]
}
, { id = 2
, points =
[ { player_id = 1, score = 20 }
, { player_id = 2, score = 5 }
, { player_id = 3, score = 0 }
]
}
, { id = 3
, points =
[ { player_id = 1, score = 20 }
, { player_id = 2, score = 5 }
, { player_id = 3, score = 10 }
]
}
]
I have a list of 'games' records which each have a list of points for each player.
Is it possible to fold each score of each player across each game to display a 'total'.
Something like:
[ { player_id = 1, score = 60 }
, { player_id = 2, score = 20 }
, { player_id = 3, score = 10 }
]
Thanks in advance.

Answer 1

You need a double fold, where the key code is
main : Html msg
main =
let
go { points } acc =
let
goInner { player_id, score } accInner =
Dict.update player_id (updater score) accInner
in
List.foldl goInner acc points
in
List.foldl go Dict.empty games
|> toString
|> text
updater : Int -> Maybe Int -> Maybe Int
updater score existingVal =
existingVal
|> Maybe.withDefault 0
|> (+) score
|> Just
See [https://ellie-app.com/gq8VFfS8Ja1/0](this ellie)
This gets you the answer you want albeit in a slightly different format