[Repo Assist] perf+feat: optimize exists/contains; add TaskSeq.distinct/distinctBy/distinctByAsync

release-notes.txt

@@ -5,6 +5,10 @@ Release notes:
     - update engineering to .NET 9/10
     - adds TaskSeq.scan and TaskSeq.scanAsync, #289
     - adds TaskSeq.pairwise, #289
+    - adds TaskSeq.reduce and TaskSeq.reduceAsync, #289
+    - adds TaskSeq.unfold and TaskSeq.unfoldAsync, #289
+    - adds TaskSeq.distinct, TaskSeq.distinctBy, TaskSeq.distinctByAsync
+    - performance: TaskSeq.exists, existsAsync, contains no longer allocate an intermediate Option value
 
 0.4.0
     - overhaul all doc comments, add exceptions, improve IDE quick-info experience, #136, #220, #234

src/FSharp.Control.TaskSeq.Test/FSharp.Control.TaskSeq.Test.fsproj

@@ -20,6 +20,7 @@
     <Compile Include="TaskSeq.ExactlyOne.Tests.fs" />
     <Compile Include="TaskSeq.Except.Tests.fs" />
     <Compile Include="TaskSeq.DistinctUntilChanged.Tests.fs" />
+    <Compile Include="TaskSeq.Distinct.Tests.fs" />
     <Compile Include="TaskSeq.Pairwise.Tests.fs" />
     <Compile Include="TaskSeq.Exists.Tests.fs" />
     <Compile Include="TaskSeq.Filter.Tests.fs" />

src/FSharp.Control.TaskSeq.Test/TaskSeq.Distinct.Tests.fs

@@ -0,0 +1,249 @@
+module TaskSeq.Tests.Distinct
+
+open Xunit
+open FsUnit.Xunit
+
+open FSharp.Control
+
+//
+// TaskSeq.distinct
+// TaskSeq.distinctBy
+// TaskSeq.distinctByAsync
+//
+
+
+module EmptySeq =
+    [<Fact>]
+    let ``TaskSeq-distinct with null source raises`` () = assertNullArg <| fun () -> TaskSeq.distinct null
+
+    [<Fact>]
+    let ``TaskSeq-distinctBy with null source raises`` () = assertNullArg <| fun () -> TaskSeq.distinctBy id null
+
+    [<Fact>]
+    let ``TaskSeq-distinctByAsync with null source raises`` () =
+        assertNullArg
+        <| fun () -> TaskSeq.distinctByAsync (fun x -> Task.fromResult x) null
+
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-distinct on empty returns empty`` variant =
+        Gen.getEmptyVariant variant
+        |> TaskSeq.distinct
+        |> verifyEmpty
+
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-distinctBy on empty returns empty`` variant =
+        Gen.getEmptyVariant variant
+        |> TaskSeq.distinctBy id
+        |> verifyEmpty
+
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-distinctByAsync on empty returns empty`` variant =
+        Gen.getEmptyVariant variant
+        |> TaskSeq.distinctByAsync (fun x -> Task.fromResult x)
+        |> verifyEmpty
+
+
+module Functionality =
+    [<Fact>]
+    let ``TaskSeq-distinct removes duplicate ints`` () = task {
+        let! result =
+            taskSeq { yield! [ 1; 2; 2; 3; 1; 4; 3; 5 ] }
+            |> TaskSeq.distinct
+            |> TaskSeq.toListAsync
+
+        result |> should equal [ 1; 2; 3; 4; 5 ]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinct removes duplicate strings`` () = task {
+        let! result =
+            taskSeq { yield! [ "a"; "b"; "b"; "a"; "c" ] }
+            |> TaskSeq.distinct
+            |> TaskSeq.toListAsync
+
+        result |> should equal [ "a"; "b"; "c" ]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinct with all identical elements returns singleton`` () = task {
+        let! result =
+            taskSeq { yield! [ 7; 7; 7; 7; 7 ] }
+            |> TaskSeq.distinct
+            |> TaskSeq.toListAsync
+
+        result |> should equal [ 7 ]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinct with all distinct elements returns all`` () = task {
+        let! result =
+            taskSeq { yield! [ 1..5 ] }
+            |> TaskSeq.distinct
+            |> TaskSeq.toListAsync
+
+        result |> should equal [ 1; 2; 3; 4; 5 ]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinct on singleton returns singleton`` () = task {
+        let! result =
+            taskSeq { yield 42 }
+            |> TaskSeq.distinct
+            |> TaskSeq.toListAsync
+
+        result |> should equal [ 42 ]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinct keeps first occurrence, not last`` () = task {
+        // sequence [3;1;2;1;3] - first occurrences are at indices 0,1,2 for values 3,1,2
+        let! result =
+            taskSeq { yield! [ 3; 1; 2; 1; 3 ] }
+            |> TaskSeq.distinct
+            |> TaskSeq.toListAsync
+
+        result |> should equal [ 3; 1; 2 ]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinct is different from distinctUntilChanged`` () = task {
+        // [1;2;1] - distinct gives [1;2], distinctUntilChanged gives [1;2;1]
+        let! distinct =
+            taskSeq { yield! [ 1; 2; 1 ] }
+            |> TaskSeq.distinct
+            |> TaskSeq.toListAsync
+
+        let! distinctUntilChanged =
+            taskSeq { yield! [ 1; 2; 1 ] }
+            |> TaskSeq.distinctUntilChanged
+            |> TaskSeq.toListAsync
+
+        distinct |> should equal [ 1; 2 ]
+        distinctUntilChanged |> should equal [ 1; 2; 1 ]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinctBy removes elements with duplicate projected keys`` () = task {
+        let! result =
+            taskSeq { yield! [ 1; 2; 3; 4; 5; 6 ] }
+            |> TaskSeq.distinctBy (fun x -> x % 3)
+            |> TaskSeq.toListAsync
+
+        // keys: 1%3=1, 2%3=2, 3%3=0, 4%3=1(dup), 5%3=2(dup), 6%3=0(dup)
+        result |> should equal [ 1; 2; 3 ]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinctBy with string length as key`` () = task {
+        let! result =
+            taskSeq { yield! [ "a"; "bb"; "c"; "dd"; "eee" ] }
+            |> TaskSeq.distinctBy String.length
+            |> TaskSeq.toListAsync
+
+        // lengths: 1, 2, 1(dup), 2(dup), 3
+        result |> should equal [ "a"; "bb"; "eee" ]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinctBy with identity projection equals distinct`` () = task {
+        let input = [ 1; 2; 2; 3; 1; 4 ]
+
+        let! byId =
+            taskSeq { yield! input }
+            |> TaskSeq.distinctBy id
+            |> TaskSeq.toListAsync
+
+        let! plain =
+            taskSeq { yield! input }
+            |> TaskSeq.distinct
+            |> TaskSeq.toListAsync
+
+        byId |> should equal plain
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinctBy keeps first element with a given key`` () = task {
+        let! result =
+            taskSeq { yield! [ (1, "a"); (2, "b"); (1, "c") ] }
+            |> TaskSeq.distinctBy fst
+            |> TaskSeq.toListAsync
+
+        result |> should equal [ (1, "a"); (2, "b") ]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinctByAsync removes elements with duplicate projected keys`` () = task {
+        let! result =
+            taskSeq { yield! [ 1; 2; 3; 4; 5; 6 ] }
+            |> TaskSeq.distinctByAsync (fun x -> task { return x % 3 })
+            |> TaskSeq.toListAsync
+
+        result |> should equal [ 1; 2; 3 ]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinctByAsync behaves identically to distinctBy`` () = task {
+        let input = [ 1; 2; 2; 3; 1; 4 ]
+        let projection x = x % 2
+
+        let! bySync =
+            taskSeq { yield! input }
+            |> TaskSeq.distinctBy projection
+            |> TaskSeq.toListAsync
+
+        let! byAsync =
+            taskSeq { yield! input }
+            |> TaskSeq.distinctByAsync (fun x -> task { return projection x })
+            |> TaskSeq.toListAsync
+
+        bySync |> should equal byAsync
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinct with chars`` () = task {
+        let! result =
+            taskSeq { yield! [ 'A'; 'A'; 'B'; 'Z'; 'C'; 'C'; 'Z'; 'C'; 'D'; 'D'; 'D'; 'Z' ] }
+            |> TaskSeq.distinct
+            |> TaskSeq.toListAsync
+
+        result |> should equal [ 'A'; 'B'; 'Z'; 'C'; 'D' ]
+    }
+
+
+module SideEffects =
+    [<Fact>]
+    let ``TaskSeq-distinct evaluates elements lazily`` () = task {
+        let mutable sideEffects = 0
+
+        let ts = taskSeq {
+            for i in 1..5 do
+                sideEffects <- sideEffects + 1
+                yield i
+        }
+
+        let distinct = ts |> TaskSeq.distinct
+
+        // no evaluation yet
+        sideEffects |> should equal 0
+
+        let! _ = distinct |> TaskSeq.toListAsync
+
+        // only evaluated when consumed
+        sideEffects |> should equal 5
+    }
+
+    [<Fact>]
+    let ``TaskSeq-distinctBy evaluates projection lazily`` () = task {
+        let mutable projections = 0
+
+        let! result =
+            taskSeq { yield! [ 1; 2; 3; 1; 2 ] }
+            |> TaskSeq.distinctBy (fun x ->
+                projections <- projections + 1
+                x)
+            |> TaskSeq.toListAsync
+
+        result |> should equal [ 1; 2; 3 ]
+        // projection called once per element (5 elements)
+        projections |> should equal 5
+    }

src/FSharp.Control.TaskSeq/TaskSeq.fs

@@ -361,23 +361,21 @@ type TaskSeq private () =
     static member except itemsToExclude source = Internal.except itemsToExclude source
     static member exceptOfSeq itemsToExclude source = Internal.exceptOfSeq itemsToExclude source
 
+    static member distinct source = Internal.distinct source
+    static member distinctBy projection source = Internal.distinctBy projection source
+    static member distinctByAsync projection source = Internal.distinctByAsync projection source
+
     static member distinctUntilChanged source = Internal.distinctUntilChanged source
     static member pairwise source = Internal.pairwise source
 
     static member forall predicate source = Internal.forall (Predicate predicate) source
     static member forallAsync predicate source = Internal.forall (PredicateAsync predicate) source
 
-    static member exists predicate source =
-        Internal.tryFind (Predicate predicate) source
-        |> Task.map Option.isSome
+    static member exists predicate source = Internal.exists (Predicate predicate) source
 
-    static member existsAsync predicate source =
-        Internal.tryFind (PredicateAsync predicate) source
-        |> Task.map Option.isSome
+    static member existsAsync predicate source = Internal.exists (PredicateAsync predicate) source
 
-    static member contains value source =
-        Internal.tryFind (Predicate((=) value)) source
-        |> Task.map Option.isSome
+    static member contains value source = Internal.contains value source
 
     static member pick chooser source =
         Internal.tryPick (TryPick chooser) source

src/FSharp.Control.TaskSeq/TaskSeq.fsi

@@ -1325,6 +1325,62 @@ type TaskSeq =
     /// <exception cref="T:ArgumentNullException">Thrown when either of the two input task sequences is null.</exception>
     static member exceptOfSeq<'T when 'T: equality> : itemsToExclude: seq<'T> -> source: TaskSeq<'T> -> TaskSeq<'T>
 
+    /// <summary>
+    /// Returns a new task sequence that contains no duplicate entries, using generic hash and equality comparisons.
+    /// If an element occurs multiple times in the sequence, only the first occurrence is returned.
+    /// </summary>
+    ///
+    /// <remarks>
+    /// This function iterates the whole sequence and buffers all unique elements in a hash set, so it should not
+    /// be used on potentially infinite sequences.
+    /// </remarks>
+    ///
+    /// <param name="source">The input task sequence.</param>
+    /// <returns>A sequence with duplicate elements removed.</returns>
+    ///
+    /// <exception cref="T:ArgumentNullException">Thrown when the input task sequence is null.</exception>
+    static member distinct<'T when 'T: equality> : source: TaskSeq<'T> -> TaskSeq<'T>
+
+    /// <summary>
+    /// Returns a new task sequence that contains no duplicate entries according to the generic hash and equality
+    /// comparisons on the keys returned by the given projection function.
+    /// If two elements have the same projected key, only the first occurrence is returned.
+    /// If the projection function is asynchronous, consider using <see cref="TaskSeq.distinctByAsync" />.
+    /// </summary>
+    ///
+    /// <remarks>
+    /// This function iterates the whole sequence and buffers all unique keys in a hash set, so it should not
+    /// be used on potentially infinite sequences.
+    /// </remarks>
+    ///
+    /// <param name="projection">A function that transforms each element to a key that is used for equality comparison.</param>
+    /// <param name="source">The input task sequence.</param>
+    /// <returns>A sequence with elements whose projected keys are distinct.</returns>
+    ///
+    /// <exception cref="T:ArgumentNullException">Thrown when the input task sequence is null.</exception>
+    static member distinctBy<'T, 'Key when 'Key: equality> :
+        projection: ('T -> 'Key) -> source: TaskSeq<'T> -> TaskSeq<'T>
+
+    /// <summary>
+    /// Returns a new task sequence that contains no duplicate entries according to the generic hash and equality
+    /// comparisons on the keys returned by the given asynchronous projection function.
+    /// If two elements have the same projected key, only the first occurrence is returned.
+    /// If the projection function is synchronous, consider using <see cref="TaskSeq.distinctBy" />.
+    /// </summary>
+    ///
+    /// <remarks>
+    /// This function iterates the whole sequence and buffers all unique keys in a hash set, so it should not
+    /// be used on potentially infinite sequences.
+    /// </remarks>
+    ///
+    /// <param name="projection">An asynchronous function that transforms each element to a key used for equality comparison.</param>
+    /// <param name="source">The input task sequence.</param>
+    /// <returns>A sequence with elements whose projected keys are distinct.</returns>
+    ///
+    /// <exception cref="T:ArgumentNullException">Thrown when the input task sequence is null.</exception>
+    static member distinctByAsync:
+        projection: ('T -> #Task<'Key>) -> source: TaskSeq<'T> -> TaskSeq<'T> when 'Key: equality
+
     /// <summary>
     /// Returns a new task sequence without consecutive duplicate elements.
     /// </summary>