Janiczek/elm-bidict

A dictionary data structure allowing for many-to-one, one-to-many and many-to-many relationships.

These, along with the ordinary Dict, give you all the relations you might need:

• one-to-one: Dict
• many-to-one: BiDict
• one-to-many: MultiDict
• many-to-many: MultiBiDict

The many-to-* variants allow you to ask for the reverse mapping (from values to keys) - see the getReverse functions.

There are both a Dict-using and an assoc-list-using variant for each of these. Thus, one needs comparable keys and values and the other can hold any types, but has slightly worse performance characteristics.

Many to one - BiDict

manyToOne : BiDict String Int
manyToOne =
    BiDict.empty
        |> BiDict.insert "A" 1
        |> BiDict.insert "B" 2
        |> BiDict.insert "C" 1
        |> BiDict.insert "D" 4

BiDict.getReverse 1 manyToOne
--> Set.fromList ["A", "C"]

One to many - MultiDict

oneToMany : MultiDict String Int
oneToMany =
    MultiDict.empty
        |> MultiDict.insert "A" 1
        |> MultiDict.insert "B" 2
        |> MultiDict.insert "A" 3
        |> MultiDict.insert "D" 4

MultiDict.get "A" oneToMany
--> Set.fromList [1, 3]

Many to many - MultiBiDict

manyToMany : MultiBiDict String Int
manyToMany =
    MultiBiDict.empty
        |> MultiBiDict.insert "A" 1
        |> MultiBiDict.insert "B" 2
        |> MultiBiDict.insert "C" 3
        |> MultiBiDict.insert "A" 2

MultiBiDict.get "A" manyToMany
--> Set.fromList [1, 2]

MultiBiDict.getReverse 2 manyToMany
--> Set.fromList ["A", "B"]