Filter_with_index, changelog

app/gui/CHANGELOG.md

@@ -17,6 +17,7 @@
 
 - [Implemented `Vector.distinct` allowing to remove duplicate elements from a
   Vector][3224]
+- [Improved performance of `Vector.filter` and `Vector.each`; implemented `Vector.filter_with_index`. Made `Vector.at` accept negative indices and ensured it fails with a dataflow error on out of bounds access instead of an internal Java exception.][3232]
 
 [3153]: https://github.com/enso-org/enso/pull/3153
 [3166]: https://github.com/enso-org/enso/pull/3166
@@ -25,6 +26,7 @@
 [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
+[3232]: https://github.com/enso-org/enso/pull/3232
 
 # Enso 2.0.0-alpha.18 (2021-10-12)
 

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

@@ -334,6 +334,30 @@ type Vector
         case acc of
             _ -> builder.to_vector
 
+    ## Selects all elements of this vector which satisfy a predicate.
+
+       Arguments:
+       - predicate: A function that takes an index and a list element and
+         returns a boolean value that says whether that value should be included
+         in the result.
+
+       > Example
+         Selecting all elements which are equal to their position in the vector.
+
+             [0, 10, 2, 2].filter (==) == [0, 2]
+    filter_with_index : (Integer -> Any -> Boolean) -> Vector Any
+    filter_with_index predicate =
+        builder = here.new_builder
+        acc = this.fold 0 ix-> elem->
+            ## The accumulator is threaded through to preserve dataflow
+               dependencies which are cut by using the stateful builder. This to
+               ensure correct dataflow error propagation.
+            acc = if predicate ix elem then builder.append elem
+            case acc of
+                _ -> ix+1
+        case acc of
+            _ -> builder.to_vector
+
     ## Applies a function to each element of the vector, returning the vector of
        results.
 

test/Tests/src/Data/Vector_Spec.enso

@@ -87,10 +87,15 @@ spec = Test.group "Vectors" <|
 
     Test.specify "should filter elements" <|
         vec = [1, 2, 3, 4, 5]
-        vec.filter (ix -> ix > 3) . should_equal [4, 5]
-        vec.filter (ix -> ix == 1) . should_equal [1]
-        vec.filter (ix -> ix < 0) . should_equal []
-        vec.filter (ix -> if ix == 2 then Error.throw <| My_Error "foo" else True) . should_fail_with My_Error
+        vec.filter (x -> x > 3) . should_equal [4, 5]
+        vec.filter (x -> x == 1) . should_equal [1]
+        vec.filter (x -> x < 0) . should_equal []
+        vec.filter (x -> if x == 2 then Error.throw <| My_Error "foo" else True) . should_fail_with My_Error
+
+    Test.specify "should filter elements with indices" <|
+        [0, 10, 2, 2].filter_with_index (==) . should_equal [0, 2]
+        ([1, 2, 3, 4].filter_with_index ix-> _-> ix < 2) . should_equal [1, 2]
+        ([1, 2, 3, 4].filter_with_index ix-> _-> if ix == 1 then Error.throw <| My_Error "foo" else True) . should_fail_with My_Error
 
     Test.specify "should allow mapping an operation, returning a new vector" <|
         vec = [1, 2, 3, 4]