Added function: frequencies (#163)

* Added function: frequencies * Update Tests.elm Forgot closing bracket * Update Tests.elm Co-authored-by: Cristian Iorga <cristian.iorga@devnest.ro> Co-authored-by: Chadtech <chadtech0@gmail.com>
elm-community · Oct 31, 2022 · b88b36f · b88b36f
1 parent ce86bf7
commit b88b36f
Show file tree

Hide file tree

Showing 2 changed files with 77 additions and 3 deletions.
diff --git a/src/List/Extra.elm b/src/List/Extra.elm
@@ -3,7 +3,7 @@ module List.Extra exposing
     , intercalate, transpose, subsequences, permutations, interweave, cartesianProduct, uniquePairs
     , foldl1, foldr1, indexedFoldl, indexedFoldr, Step(..), stoppableFoldl
     , scanl, scanl1, scanr, scanr1, mapAccuml, mapAccumr, unfoldr, iterate, initialize, cycle, reverseRange
-    , splitAt, splitWhen, takeWhileRight, dropWhileRight, span, break, stripPrefix, group, groupWhile, inits, tails, select, selectSplit, gatherEquals, gatherEqualsBy, gatherWith, subsequencesNonEmpty
+    , splitAt, splitWhen, takeWhileRight, dropWhileRight, span, break, stripPrefix, group, groupWhile, inits, tails, select, selectSplit, gatherEquals, gatherEqualsBy, gatherWith, subsequencesNonEmpty, frequencies
     , isPrefixOf, isSuffixOf, isInfixOf, isSubsequenceOf, isPermutationOf
     , notMember, find, elemIndex, elemIndices, findIndex, findIndices, findMap, count
     , zip, zip3
@@ -37,7 +37,7 @@ module List.Extra exposing
 
 # Sublists
 
-@docs splitAt, splitWhen, takeWhileRight, dropWhileRight, span, break, stripPrefix, group, groupWhile, inits, tails, select, selectSplit, gatherEquals, gatherEqualsBy, gatherWith, subsequencesNonEmpty
+@docs splitAt, splitWhen, takeWhileRight, dropWhileRight, span, break, stripPrefix, group, groupWhile, inits, tails, select, selectSplit, gatherEquals, gatherEqualsBy, gatherWith, subsequencesNonEmpty, frequencies
 
 
 # Predicates
@@ -2140,6 +2140,22 @@ gatherWith testFn list =
     helper list []
 
 
+{-| Calculate the number of occurences for each element in a list. Elements
+will be ordered ascendingly, then grouped in a tuple with the number of
+occurences.
+
+    frequencies [2,1,3,2,3,3]
+    --> [(1,1),(2,2),(3,3)]
+
+-}
+frequencies : List comparable -> List ( comparable, Int )
+frequencies list =
+    list
+        |> List.sort
+        |> group
+        |> List.map (\( x, y ) -> ( x, 1 + List.length y ))
+
+
 {-| Performs an inner join, combining data items from both lists if they match by their respective key functions.
 
     employees : List { name : String, departmentId : Int }

diff --git a/tests/Tests.elm b/tests/Tests.elm
@@ -1018,6 +1018,64 @@ all =
                     joinOn Tuple.pair identity identity [ 1, 3, 2 ] [ 2, 1, 3 ]
                         |> Expect.equal [ ( 3, 3 ), ( 2, 2 ), ( 1, 1 ) ]
             ]
+        , describe "frequencies"
+            [ describe "Property testing with fuzz"
+                [ fuzz (list int) "Final value similar list and List.sort list" <|
+                    \list ->
+                        frequencies list
+                            |> List.sort
+                            |> Expect.equal (frequencies list)
+                , fuzz (list int) "Final value similar, no matter the order of composition for frequencies and List.sort" <|
+                    \list ->
+                        let
+                            freqFirst =
+                                list
+                                    |> frequencies
+                                    |> List.sort
+
+                            sortFirst =
+                                list
+                                    |> List.sort
+                                    |> frequencies
+                        in
+                        freqFirst
+                            |> Expect.equal sortFirst
+                , fuzz2 (list int) (list int) "Two (different/similar) lists should give 2 (different/similar) results" <|
+                    \list1 list2 ->
+                        let
+                            areListsSimilar =
+                                isPermutationOf list2 list1
+
+                            freq1 =
+                                frequencies list1
+
+                            freq2 =
+                                frequencies list2
+
+                            shouldFreqsBeSimilar =
+                                areListsSimilar
+
+                            areFreqsSimilar =
+                                isPermutationOf freq2 freq1
+                        in
+                        areFreqsSimilar
+                            |> Expect.equal shouldFreqsBeSimilar
+                ]
+            , describe "Unit testing on basic examples"
+                [ test "Frequencies on List Int" <|
+                    \() ->
+                        frequencies [ 4, 1, 3, 2, 2, 4, 3, 3, 4, 4 ]
+                            |> Expect.equal [ ( 1, 1 ), ( 2, 2 ), ( 3, 3 ), ( 4, 4 ) ]
+                , test "Frequencies on List String" <|
+                    \() ->
+                        frequencies [ "a", "b", "aa", "c", "b", "aa", "c", "C", "C", "D" ]
+                            |> Expect.equal [ ( "C", 2 ), ( "D", 1 ), ( "a", 1 ), ( "aa", 2 ), ( "b", 2 ), ( "c", 2 ) ]
+                , test "Frequencies on empty List a" <|
+                    \() ->
+                        frequencies []
+                            |> Expect.equal []
+                ]
+            ]
         , describe "stoppableFoldl"
             [ fuzz (list int) "behaves like foldl if function always returns Continue" <|
                 \xs ->
@@ -1056,7 +1114,7 @@ all =
                                 Stop n
 
                             else
-                                explode ()
+                                throwRangeErrorException ()
                         )
                         0
                         (List.range 1 1000)