Adds Dict.Extra.{invertAll,upsert,updateIfExists} (#62)

src/Dict/Extra.elm

@@ -1,6 +1,7 @@
 module Dict.Extra exposing
  ( groupBy, filterGroupBy, fromListBy, fromListCombining, fromListByCombining, frequencies
- , removeWhen, removeMany, keepOnly, insertCombining, mapKeys, filterMap, invert
+ , removeWhen, removeMany, keepOnly, insertCombining, updateIfExists, upsert, invert, invertAll
+ , mapKeys, filterMap
  , any, all
  , find
  , unionWith
@@ -16,7 +17,12 @@ module Dict.Extra exposing
 
 # Manipulation
 
-@docs removeWhen, removeMany, keepOnly, insertCombining, mapKeys, filterMap, invert
+@docs removeWhen, removeMany, keepOnly, insertCombining, updateIfExists, upsert, invert, invertAll
+
+
+# Maps
+
+@docs mapKeys, filterMap
 
 
 # Predicates
@@ -243,6 +249,46 @@ insertCombining combine key value dict =
  Dict.update key with dict
 
 
+{-| Updates a value if the key is present in the dictionary, leaves the dictionary untouched otherwise.
+
+ import Dict
+
+ Dict.fromList [ ( "expenses", 38.25 ), ( "assets", 100.85 ) ]
+ |> updateIfExists "expenses" (\amount -> amount + 2.50)
+ |> updateIfExists "liabilities" (\amount -> amount - 2.50)
+ --> Dict.fromList [ ( "expenses", 40.75 ), ( "assets", 100.85 ) ]
+
+-}
+updateIfExists : comparable -> (a -> a) -> Dict comparable a -> Dict comparable a
+updateIfExists key f dict =
+ case Dict.get key dict of
+ Just value ->
+ Dict.insert key (f value) dict
+
+ Nothing ->
+ dict
+
+
+{-| Updates a value if the key is present in the dictionary, inserts a new key-value pair otherwise.
+
+ import Dict
+
+ Dict.fromList [ ( "expenses", 38.25 ), ( "assets", 100.85 ) ]
+ |> upsert "expenses" 4.50 (\amount -> amount + 2.50)
+ |> upsert "liabilities" 2.50 (\amount -> amount - 2.50)
+ --> Dict.fromList [ ( "expenses", 40.75 ), ( "assets", 100.85 ), ( "liabilities", 2.50 ) ]
+
+-}
+upsert : comparable -> a -> (a -> a) -> Dict comparable a -> Dict comparable a
+upsert key value f dict =
+ case Dict.get key dict of
+ Just oldValue ->
+ Dict.insert key (f oldValue) dict
+
+ Nothing ->
+ Dict.insert key value dict
+
+
 {-| Keep a key-value pair if its key appears in the set.
 
  import Dict
@@ -337,6 +383,31 @@ invert dict =
  dict
 
 
+{-| Like `invert`, it changes the keys and values. However, if one value maps to multiple keys, then all of the keys will be retained.
+
+ import Dict
+ import Set
+
+ Dict.fromList [ ( 1, "Jill" ), ( 2, "Jill" ), ( 3, "Jack" ) ]
+ |> invertAll
+ --> Dict.fromList [ ( "Jill", Set.fromList [ 1, 2 ] ), ( "Jack", Set.singleton 3 ) ]
+
+-}
+invertAll : Dict comparable1 comparable2 -> Dict comparable2 (Set comparable1)
+invertAll dict =
+ Dict.foldl
+ (\k v acc ->
+ case Dict.get v acc of
+ Just set ->
+ Dict.insert v (Set.insert k set) acc
+
+ Nothing ->
+ Dict.insert v (Set.singleton k) acc
+ )
+ Dict.empty
+ dict
+
+
 {-| Determine if any key/value pair satisfies some test.
 
  import Dict

tests/DictTests.elm

@@ -0,0 +1,44 @@
+module DictTests exposing (suite)
+
+import Dict
+import Dict.Extra
+import Expect
+import Fuzz exposing (Fuzzer)
+import Set
+import Set.Extra
+import Test exposing (Test, describe)
+
+
+dictFuzzer : Fuzzer comparable -> Fuzzer v -> Fuzzer (Dict.Dict comparable v)
+dictFuzzer keyFuzzer valueFuzzer =
+ Fuzz.map Dict.fromList (Fuzz.list (Fuzz.pair keyFuzzer valueFuzzer))
+
+
+suite : Test
+suite =
+ describe "Dict.Extra"
+ [ describe "invertAll"
+ [ Test.fuzz (dictFuzzer Fuzz.string Fuzz.int) "does not loose information" <|
+ \dict ->
+ dict
+ |> Dict.Extra.invertAll
+ |> Dict.map (always Set.size)
+ |> Dict.values
+ |> List.sum
+ |> Expect.equal (Dict.size dict)
+ , Test.fuzz (dictFuzzer Fuzz.string Fuzz.int) "the values are keys into the original dictionary" <|
+ \dict ->
+ dict
+ |> Dict.Extra.invertAll
+ |> Dict.Extra.all
+ (\key vals ->
+ Set.Extra.all (\val -> Dict.get val dict == Just key) vals
+ )
+ |> Expect.equal True
+ , Test.fuzz (Fuzz.map Dict.Extra.invert (dictFuzzer Fuzz.string Fuzz.int)) "behaves the same as invert on an already inverted dictionary" <|
+ \dict ->
+ dict
+ |> Dict.Extra.invertAll
+ |> Expect.equal (dict |> Dict.Extra.invert |> Dict.map (always Set.singleton))
+ ]
+ ]