FS-1135 implementation - random functions for collections

docs/release-notes/.FSharp.Core/8.0.400.md

@@ -2,6 +2,8 @@
 
 ### Added
 
+* `Random functions for collections` ([RFC #1135](https://github.com/fsharp/fslang-design/blob/main/RFCs/FS-1135-random-functions-for-collections.md), [PR #17277](https://github.com/dotnet/fsharp/pull/17277))
+
 ### Changed
 
 * Cache delegate in query extensions. ([PR #17130](https://github.com/dotnet/fsharp/pull/17130))

src/FSharp.Core/FSharp.Core.fsproj

@@ -91,6 +91,12 @@
     <Compile Include="prim-types.fs">
       <Link>Primitives/prim-types.fs</Link>
     </Compile>
+    <Compile Include="Random.fsi">
+      <Link>Random/Random.fsi</Link>
+    </Compile>
+    <Compile Include="Random.fs">
+      <Link>Random/Random.fs</Link>
+    </Compile>
     <Compile Include="local.fsi">
       <Link>Collections/local.fsi</Link>
     </Compile>

src/FSharp.Core/Random.fs

@@ -0,0 +1,25 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Microsoft.FSharp.Core
+
+open System
+open System.Runtime.CompilerServices
+open System.Threading
+
+[<AbstractClass; Sealed>]
+type internal ThreadSafeRandom() =
+
+    [<DefaultValue>]
+    [<ThreadStatic>]
+    static val mutable private random: Random
+
+    [<MethodImpl(MethodImplOptions.NoInlining)>]
+    static member private Create() =
+        ThreadSafeRandom.random <- Random()
+        ThreadSafeRandom.random
+
+    // Don't pass the returned Random object between threads
+    static member Shared =
+        match ThreadSafeRandom.random with
+        | null -> ThreadSafeRandom.Create()
+        | random -> random

src/FSharp.Core/Random.fsi

@@ -0,0 +1,7 @@
+namespace Microsoft.FSharp.Core
+
+open System
+
+[<AbstractClass; Sealed>]
+type internal ThreadSafeRandom =
+    static member Shared: Random

src/FSharp.Core/array.fs

@@ -1936,6 +1936,211 @@ module Array =
 
             result
 
+    [<CompiledName("RandomShuffleWith")>]
+    let randomShuffleWith (random: Random) (source: 'T array) : 'T array =
+        checkNonNull "random" random
+        checkNonNull "source" source
+
+        let result = copy source
+
+        Microsoft.FSharp.Primitives.Basics.Random.shuffleArrayInPlaceWith random result
+
+        result
+
+    [<CompiledName("RandomShuffleBy")>]
+    let randomShuffleBy (randomizer: unit -> float) (source: 'T array) : 'T array =
+        checkNonNull "source" source
+
+        let result = copy source
+
+        Microsoft.FSharp.Primitives.Basics.Random.shuffleArrayInPlaceBy randomizer result
+
+        result
+
+    [<CompiledName("RandomShuffle")>]
+    let randomShuffle (source: 'T array) : 'T array =
+        randomShuffleWith ThreadSafeRandom.Shared source
+
+    [<CompiledName("RandomShuffleInPlaceWith")>]
+    let randomShuffleInPlaceWith (random: Random) (source: 'T array) =
+        checkNonNull "random" random
+        checkNonNull "source" source
+
+        Microsoft.FSharp.Primitives.Basics.Random.shuffleArrayInPlaceWith random source
+
+    [<CompiledName("RandomShuffleInPlaceBy")>]
+    let randomShuffleInPlaceBy (randomizer: unit -> float) (source: 'T array) =
+        checkNonNull "source" source
+
+        Microsoft.FSharp.Primitives.Basics.Random.shuffleArrayInPlaceBy randomizer source
+
+    [<CompiledName("RandomShuffleInPlace")>]
+    let randomShuffleInPlace (source: 'T array) =
+        randomShuffleInPlaceWith ThreadSafeRandom.Shared source
+
+    [<CompiledName("RandomChoiceWith")>]
+    let randomChoiceWith (random: Random) (source: 'T array) : 'T =
+        checkNonNull "random" random
+        checkNonNull "source" source
+
+        let inputLength = source.Length
+
+        if inputLength = 0 then
+            invalidArg "source" LanguagePrimitives.ErrorStrings.InputArrayEmptyString
+
+        let i = random.Next(0, inputLength)
+        source[i]
+
+    [<CompiledName("RandomChoiceBy")>]
+    let randomChoiceBy (randomizer: unit -> float) (source: 'T array) : 'T =
+        checkNonNull "source" source
+
+        let inputLength = source.Length
+
+        if inputLength = 0 then
+            invalidArg "source" LanguagePrimitives.ErrorStrings.InputArrayEmptyString
+
+        let i = Microsoft.FSharp.Primitives.Basics.Random.next randomizer 0 inputLength
+        source[i]
+
+    [<CompiledName("RandomChoice")>]
+    let randomChoice (source: 'T array) : 'T =
+        randomChoiceWith ThreadSafeRandom.Shared source
+
+    [<CompiledName("RandomChoicesWith")>]
+    let randomChoicesWith (random: Random) (count: int) (source: 'T array) : 'T array =
+        checkNonNull "random" random
+        checkNonNull "source" source
+
+        if count < 0 then
+            invalidArgInputMustBeNonNegative "count" count
+
+        let inputLength = source.Length
+
+        if inputLength = 0 then
+            invalidArg "source" LanguagePrimitives.ErrorStrings.InputArrayEmptyString
+
+        let result = Microsoft.FSharp.Primitives.Basics.Array.zeroCreateUnchecked count
+
+        for i = 0 to count - 1 do
+            let j = random.Next(0, inputLength)
+            result[i] <- source[j]
+
+        result
+
+    [<CompiledName("RandomChoicesBy")>]
+    let randomChoicesBy (randomizer: unit -> float) (count: int) (source: 'T array) : 'T array =
+        checkNonNull "source" source
+
+        if count < 0 then
+            invalidArgInputMustBeNonNegative "count" count
+
+        let inputLength = source.Length
+
+        if inputLength = 0 then
+            invalidArg "source" LanguagePrimitives.ErrorStrings.InputArrayEmptyString
+
+        let result = Microsoft.FSharp.Primitives.Basics.Array.zeroCreateUnchecked count
+
+        for i = 0 to count - 1 do
+            let j = Microsoft.FSharp.Primitives.Basics.Random.next randomizer 0 inputLength
+            result[i] <- source[j]
+
+        result
+
+    [<CompiledName("RandomChoices")>]
+    let randomChoices (count: int) (source: 'T array) : 'T array =
+        randomChoicesWith ThreadSafeRandom.Shared count source
+
+    [<CompiledName("RandomSampleWith")>]
+    let randomSampleWith (random: Random) (count: int) (source: 'T array) : 'T array =
+        checkNonNull "random" random
+        checkNonNull "source" source
+
+        if count < 0 then
+            invalidArgInputMustBeNonNegative "count" count
+
+        let inputLength = source.Length
+
+        if inputLength = 0 then
+            invalidArg "source" LanguagePrimitives.ErrorStrings.InputArrayEmptyString
+
+        if count > inputLength then
+            invalidArg "count" (SR.GetString(SR.notEnoughElements))
+
+        let result = Microsoft.FSharp.Primitives.Basics.Array.zeroCreateUnchecked count
+
+        let setSize =
+            Microsoft.FSharp.Primitives.Basics.Random.getMaxSetSizeForSampling count
+
+        if inputLength <= setSize then
+            let pool = copy source
+
+            for i = 0 to count - 1 do
+                let j = random.Next(0, inputLength - i)
+                result[i] <- pool[j]
+                pool[j] <- pool[inputLength - i - 1]
+        else
+            let selected = HashSet()
+
+            for i = 0 to count - 1 do
+                let mutable j = random.Next(0, inputLength)
+
+                while not (selected.Add j) do
+                    j <- random.Next(0, inputLength)
+
+                result[i] <- source[j]
+
+        result
+
+    [<CompiledName("RandomSampleBy")>]
+    let randomSampleBy (randomizer: unit -> float) (count: int) (source: 'T array) : 'T array =
+        checkNonNull "source" source
+
+        if count < 0 then
+            invalidArgInputMustBeNonNegative "count" count
+
+        let inputLength = source.Length
+
+        if inputLength = 0 then
+            invalidArg "source" LanguagePrimitives.ErrorStrings.InputArrayEmptyString
+
+        if count > inputLength then
+            invalidArg "count" (SR.GetString(SR.notEnoughElements))
+
+        let result = Microsoft.FSharp.Primitives.Basics.Array.zeroCreateUnchecked count
+
+        // algorithm taken from https://github.com/python/cpython/blob/69b3e8ea569faabccd74036e3d0e5ec7c0c62a20/Lib/random.py#L363-L456
+        let setSize =
+            Microsoft.FSharp.Primitives.Basics.Random.getMaxSetSizeForSampling count
+
+        if inputLength <= setSize then
+            let pool = copy source
+
+            for i = 0 to count - 1 do
+                let j =
+                    Microsoft.FSharp.Primitives.Basics.Random.next randomizer 0 (inputLength - i)
+
+                result[i] <- pool[j]
+                pool[j] <- pool[inputLength - i - 1]
+        else
+            let selected = HashSet()
+
+            for i = 0 to count - 1 do
+                let mutable j =
+                    Microsoft.FSharp.Primitives.Basics.Random.next randomizer 0 inputLength
+
+                while not (selected.Add j) do
+                    j <- Microsoft.FSharp.Primitives.Basics.Random.next randomizer 0 inputLength
+
+                result[i] <- source[j]
+
+        result
+
+    [<CompiledName("RandomSample")>]
+    let randomSample (count: int) (source: 'T array) : 'T array =
+        randomSampleWith ThreadSafeRandom.Shared count source
+
     module Parallel =
         open System.Threading
         open System.Threading.Tasks