The user should be able to remove duplicate elements from a Vector

app/gui/CHANGELOG.md

@@ -13,12 +13,18 @@
 - [Fixed developer console error about failing to decode a notification
   "executionContext/visualisationEvaluationFailed"][3193]
 
+#### Enso Standard Library
+
+- [Implemented `Vector.distinct` allowing to remove duplicate elements from a
+  Vector][3224]
+
 [3153]: https://github.com/enso-org/enso/pull/3153
 [3166]: https://github.com/enso-org/enso/pull/3166
 [3181]: https://github.com/enso-org/enso/pull/3181
 [3186]: https://github.com/enso-org/enso/pull/3186
 [3193]: https://github.com/enso-org/enso/pull/3193
 [3208]: https://github.com/enso-org/enso/pull/3208
+[3224]: https://github.com/enso-org/enso/pull/3224
 
 # Enso 2.0.0-alpha.18 (2021-10-12)
 

distribution/lib/Standard/Base/0.2.32-SNAPSHOT/src/Data/Vector.enso

@@ -1,6 +1,8 @@
 from Standard.Base import all
 from Standard.Builtins import Array
 
+polyglot java import java.util.HashSet
+
 ## Creates a new vector of the given length, initializing elements using
    the provided constructor function.
 
@@ -720,6 +722,42 @@ type Vector
 
         Vector new_vec_arr
 
+    ## UNSTABLE
+       Keeps only unique elements within the Vector, removing any duplicates.
+
+       Arguments:
+       - on: A projection from the element type to the value of that element
+             which determines the uniqueness criteria.
+
+       The returned unique elements are kept in the same order as they appeared
+       in the input.
+
+       Out of multiple equivalent (equal up to the `on` projection) elements,
+       always the one appearing first in the input is kept.
+
+       > Example
+         Removing repeating entries.
+
+             [1, 3, 1, 2, 2, 1] . distinct == [1, 3, 2]
+
+       > Example
+         Keeping only pairs whose first elements are unique.
+
+             [Pair 1 "a", Pair 2 "b", Pair 1 "c"] . distinct (on = _.first) == [Pair 1 "a", Pair 2 "b"]
+    distinct : (Any -> Any) -> Vector Any
+    distinct (on = x->x) =
+        builder = here.new_builder
+        existing_elements = HashSet.new
+
+        this.each elem->
+            proj = on elem
+            if existing_elements.contains proj then Nothing else
+                existing_elements.add proj
+                builder.append elem
+
+        builder.to_vector
+
+
     ## UNSTABLE
 
        Transform the vector into text for displaying as part of its default

test/Tests/src/Data/Vector_Spec.enso

@@ -253,3 +253,19 @@ spec = Test.group "Vectors" <|
     Test.specify "should append elements" <|
         [1, 2].append 3 . should_equal [1, 2, 3]
 
+    Test.specify "should return a vector containing only unique elements" <|
+        [1, 3, 1, 2, 2, 1].distinct . should_equal [1, 3, 2]
+        ["a", "a", "a"].distinct . should_equal ["a"]
+        [].distinct . should_equal []
+
+        ["a", 2].distinct . should_equal ["a", 2]
+        [2, "a", Integer, "a", 2].distinct . should_equal [2, "a", Integer]
+
+    structural_eq_reason="Disabled until structural equality of Atoms is properly exposed through Polyglot."
+    Test.specify "should correctly handle distinct with custom types like Atoms" pending=structural_eq_reason <|
+        [T 1 2, T 3 3, T 1 2].distinct . should_equal [T 1 2, T 3 3]
+
+    Test.specify "should return a vector containing only unique elements up to some criteria" <|
+        [Pair 1 "a", Pair 2 "b", Pair 1 "c"] . distinct (on = _.first) . should_equal [Pair 1 "a", Pair 2 "b"]
+
+main = Test.Suite.run_main here.spec