Janiczek / elm-bidict / MultiBiDict

A dictionary mapping unique keys to multiple values, which maintains a mapping from the values back to keys, allowing for modelling many-to-many relationships.

Example usage:

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"]

Dictionaries


type MultiBiDict comparable1 comparable2

The underlying data structure. Think about it as

type alias MultiBiDict comparable1 comparable2 =
    { forward : Dict comparable1 (Set comparable2) -- just a normal Dict!
    , reverse : Dict comparable2 (Set comparable1) -- the reverse mappings!
    }

Differences from Dict

toDict : MultiBiDict comparable1 comparable2 -> Dict comparable1 (Set comparable2)

Convert MultiBiDict into a Dict. (Throw away the reverse mapping.)

fromDict : Dict comparable1 (Set comparable2) -> MultiBiDict comparable1 comparable2

Convert Dict into a MultiBiDict. (Compute the reverse mapping.)

getReverse : comparable2 -> MultiBiDict comparable1 comparable2 -> Set comparable1

Get the keys associated with a value. If the value is not found, return an empty set.

uniqueValues : MultiBiDict comparable1 comparable2 -> List comparable2

Get a list of unique values in the dictionary.

uniqueValuesCount : MultiBiDict comparable1 comparable2 -> Basics.Int

Get a count of unique values in the dictionary.

toReverseList : MultiBiDict comparable1 comparable2 -> List ( comparable2, Set comparable1 )

Convert a dictionary into a reverse association list of value-keys pairs.

Build

empty : MultiBiDict comparable1 comparable2

Create an empty dictionary.

singleton : comparable1 -> comparable2 -> MultiBiDict comparable1 comparable2

Create a dictionary with one key-value pair.

insert : comparable1 -> comparable2 -> MultiBiDict comparable1 comparable2 -> MultiBiDict comparable1 comparable2

Insert a key-value pair into a dictionary. Replaces value when there is a collision.

update : comparable1 -> (Set comparable2 -> Set comparable2) -> MultiBiDict comparable1 comparable2 -> MultiBiDict comparable1 comparable2

Update the value of a dictionary for a specific key with a given function.

remove : comparable1 -> comparable2 -> MultiBiDict comparable1 comparable2 -> MultiBiDict comparable1 comparable2

Remove a single key-value pair from a dictionary. If the key is not found, no changes are made.

removeAll : comparable1 -> MultiBiDict comparable1 comparable2 -> MultiBiDict comparable1 comparable2

Remove all key-value pairs for the given key from a dictionary. If the key is not found, no changes are made.

Query

isEmpty : MultiBiDict comparable1 comparable2 -> Basics.Bool

Determine if a dictionary is empty.

isEmpty empty == True

member : comparable1 -> MultiBiDict comparable1 comparable2 -> Basics.Bool

Determine if a key is in a dictionary.

get : comparable1 -> MultiBiDict comparable1 comparable2 -> Set comparable2

Get the value associated with a key. If the key is not found, return Nothing. This is useful when you are not sure if a key will be in the dictionary.

animals = fromList [ ("Tom", Cat), ("Jerry", Mouse) ]

get "Tom"   animals == Just Cat
get "Jerry" animals == Just Mouse
get "Spike" animals == Nothing

size : MultiBiDict comparable1 comparable2 -> Basics.Int

Determine the number of key-value pairs in the dictionary.

Lists

keys : MultiBiDict comparable1 comparable2 -> List comparable1

Get all of the keys in a dictionary, sorted from lowest to highest.

keys (fromList [ ( 0, "Alice" ), ( 1, "Bob" ) ]) == [ 0, 1 ]

values : MultiBiDict comparable1 comparable2 -> List comparable2

Get all of the values in a dictionary, in the order of their keys.

values (fromList [ ( 0, "Alice" ), ( 1, "Bob" ) ]) == [ "Alice", "Bob" ]

toList : MultiBiDict comparable1 comparable2 -> List ( comparable1, Set comparable2 )

Convert a dictionary into an association list of key-value pairs, sorted by keys.

fromList : List ( comparable1, Set comparable2 ) -> MultiBiDict comparable1 comparable2

Convert an association list into a dictionary.

Transform

map : (comparable1 -> comparable21 -> comparable22) -> MultiBiDict comparable1 comparable21 -> MultiBiDict comparable1 comparable22

Apply a function to all values in a dictionary.

foldl : (comparable1 -> Set comparable2 -> acc -> acc) -> acc -> MultiBiDict comparable1 comparable2 -> acc

Fold over the key-value pairs in a dictionary from lowest key to highest key.

getAges users =
    Dict.foldl addAge [] users

addAge _ user ages =
    user.age :: ages

-- getAges users == [33,19,28]

foldr : (comparable1 -> Set comparable2 -> acc -> acc) -> acc -> MultiBiDict comparable1 comparable2 -> acc

Fold over the key-value pairs in a dictionary from highest key to lowest key.

getAges users =
    Dict.foldr addAge [] users

addAge _ user ages =
    user.age :: ages

-- getAges users == [28,19,33]

filter : (comparable1 -> comparable2 -> Basics.Bool) -> MultiBiDict comparable1 comparable2 -> MultiBiDict comparable1 comparable2

Keep only the mappings that pass the given test.

partition : (comparable1 -> Set comparable2 -> Basics.Bool) -> MultiBiDict comparable1 comparable2 -> ( MultiBiDict comparable1 comparable2, MultiBiDict comparable1 comparable2 )

Partition a dictionary according to some test. The first dictionary contains all key-value pairs which passed the test, and the second contains the pairs that did not.

Combine

union : MultiBiDict comparable1 comparable2 -> MultiBiDict comparable1 comparable2 -> MultiBiDict comparable1 comparable2

Combine two dictionaries. If there is a collision, preference is given to the first dictionary.

intersect : MultiBiDict comparable1 comparable2 -> MultiBiDict comparable1 comparable2 -> MultiBiDict comparable1 comparable2

Keep a key-value pair when its key appears in the second dictionary. Preference is given to values in the first dictionary.

diff : MultiBiDict comparable1 comparable2 -> MultiBiDict comparable1 comparable2 -> MultiBiDict comparable1 comparable2

Keep a key-value pair when its key does not appear in the second dictionary.

merge : (comparable1 -> Set comparable21 -> acc -> acc) -> (comparable1 -> Set comparable21 -> Set comparable22 -> acc -> acc) -> (comparable1 -> Set comparable22 -> acc -> acc) -> MultiBiDict comparable1 comparable21 -> MultiBiDict comparable1 comparable22 -> acc -> acc

The most general way of combining two dictionaries. You provide three accumulators for when a given key appears:

  1. Only in the left dictionary.
  2. In both dictionaries.
  3. Only in the right dictionary.

You then traverse all the keys from lowest to highest, building up whatever you want.