Takes a key-fn and a list. Creates a Dict which maps the key to a list of matching elements.

import Dict


groupBy String.length [ "tree" , "apple" , "leaf" ]
--> Dict.fromList [ ( 4, [ "tree", "leaf" ] ), ( 5, [ "apple" ] ) ]

Takes a key-fn and a list. Creates a Dict which maps the key to a list of matching elements, skipping elements where key-fn returns Nothing

import Dict


filterGroupBy (String.uncons >> Maybe.map Tuple.first) [ "tree" , "", "tweet", "apple" , "leaf", "" ]
--> Dict.fromList [ ( 't', [ "tree", "tweet" ] ), ( 'a', [ "apple" ] ), ( 'l', [ "leaf" ] ) ]


filterGroupBy
    .car
    [ { name = "Mary"
      , car = Just "Ford"
      }
    , { name = "Jack"
      , car = Nothing
      }
    , { name = "Jill"
      , car = Just "Tesla"
      }
    , { name = "John"
      , car = Just "Tesla"
      }
    ]
--> Dict.fromList
    [ ( "Ford"
      , [ { name = "Mary" , car = Just "Ford" } ]
      )
    , ( "Tesla"
      , [ { name = "Jill" , car = Just "Tesla" }
        , { name = "John" , car = Just "Tesla" }
        ]
      )
    ]

Create a dictionary from a list of values, by passing a function that can get a key from any such value. If the function does not return unique keys, earlier values are discarded.

fromListBy String.length [ "tree" , "apple" , "leaf" ]
--> Dict.fromList [ ( 4, "leaf" ), ( 5, "apple" ) ]

Like Dict.fromList, but you provide a way to deal with duplicate keys. Create a dictionary from a list of pairs of keys and values, providing a function that is used to combine multiple values paired with the same key.

fromListDedupe
    (\a b -> a ++ " " ++ b)
    [ ( "class", "menu" ), ( "width", "100%" ), ( "class", "big" ) ]
--> Dict.fromList [ ( "class", "menu big" ), ( "width", "100%" ) ]

fromListBy and fromListDedupe rolled into one.

fromListDedupeBy (\first second -> first) String.length [ "tree" , "apple" , "leaf" ]
--> Dict.fromList [ ( 4, "tree" ), ( 5, "apple" ) ]

Count the number of occurences for each of the elements in the list.

frequencies [ "A", "B", "C", "B", "C", "B" ]
--> Dict.fromList [ ( "A", 1 ), ( "B", 3 ), ( "C", 2 ) ]

Remove elements which satisfies the predicate.

Dict.fromList [ ( "Mary", 1 ), ( "Jack", 2 ), ( "Jill", 1 ) ]
    |> removeWhen (\_ value -> value == 1 )
--> Dict.fromList [ ( "Jack", 2 ) ]

Remove a key-value pair if its key appears in the set.

import Set


Dict.fromList [ ( "Mary", 1 ), ( "Jack", 2 ), ( "Jill", 1 ) ]
    |> removeMany (Set.fromList [ "Mary", "Jill" ])
--> Dict.fromList [ ( "Jack", 2 ) ]

Keep a key-value pair if its key appears in the set.

Dict.fromList [ ( "Mary", 1 ), ( "Jack", 2 ), ( "Jill", 1 ) ]
    |> keepOnly (Set.fromList [ "Jack", "Jill" ])
--> Dict.fromList [ ( "Jack", 2 ), ( "Jill", 1 ) ]

Insert an element at the given key, providing a combining function that used in the case that there is already an element at that key. The combining function is called with original element and the new element as arguments and returns the element to be inserted.

Dict.fromList [ ( "expenses", 38.25 ), ( "assets", 100.85 ) ]
    |> insertDedupe (+) "expenses" 2.50
    |> insertDedupe (+) "liabilities" -2.50
--> Dict.fromList [ ( "expenses", 40.75 ), ( "assets", 100.85 ), ( "liabilities", -2.50 ) ]

Apply a function to all keys in a dictionary.

Dict.fromList [ ( 5, "Jack" ), ( 10, "Jill" ) ]
    |> mapKeys (\x -> x + 1)
--> Dict.fromList [ ( 6, "Jack" ), ( 11, "Jill" ) ]


Dict.fromList [ ( 5, "Jack" ), ( 10, "Jill" ) ]
    |> mapKeys toString
--> Dict.fromList [ ( "5", "Jack" ), ( "10", "Jill" ) ]

Apply a function that may or may not succeed to all entries in a dictionary, but only keep the successes.

let
    isTeen n a =
        if 13 <= n && n <= 19 then
            Just <| String.toUpper a
        else
            Nothing
in
    Dict.fromList [ ( 5, "Jack" ), ( 15, "Jill" ), ( 20, "Jones" ) ]
        |> filterMap isTeen
--> Dict.fromList [ ( 15, "JILL" ) ]

Inverts the keys and values of an array.

Dict.fromList [ ("key", "value")  ]
    |> invert
--> Dict.fromList [ ( "value", "key" ) ]

Find the first key/value pair that matches a predicate.

Dict.fromList [ ( 9, "Jill" ), ( 7, "Jill" ) ]
    |> find (\_ value -> value == "Jill")
--> Just ( 7, "Jill" )


Dict.fromList [ ( 9, "Jill" ), ( 7, "Jill" ) ]
    |> find (\key _ -> key == 5)
--> Nothing