Add partitionResults with single-pass destructuring (#359)

* Add partitionResult

* Use single-pass implementations for partitionResults

Address review feedback from #358: replace two-pass Array.choose
implementations with single-pass alternatives. Array uses ResizeArray,
List uses tail-recursive loop, Seq returns seq instead of array.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Implement suggested changes

* Add null guards

* rename variable

* Add docs to gitbook

* ReferenceEquals as null guard and missing xml docs

* Add Array section to Gitbook

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bpe-incom

gitbook/SUMMARY.md

@@ -26,11 +26,15 @@
       * [sequenceResultM](list/sequenceResultM.md)
       * [traverseResultA](list/traverseResultA.md)
       * [sequenceResultA](list/sequenceResultA.md)
+      * [partitionResults](list/partitionResults.md)
     * Sequences
       * [traverseResultM](seq/traverseResultM.md)
       * [sequenceResultM](seq/sequenceResultM.md)
       * [traverseResultA](seq/traverseResultA.md)
       * [sequenceResultA](seq/sequenceResultA.md)
+      * [partitionResults](seq/partitionResults.md)
+    * Arrays
+      * [partitionResults](array/partitionResults.md)
     * Transforms
       * [ofChoice](result/ofChoice.md)
 

gitbook/array/partitionResults.md

@@ -0,0 +1,53 @@
+# Array.partitionResults
+
+Namespace: `FsToolkit.ErrorHandling`
+
+## Function Signature
+
+```fsharp
+Result<'ok, 'error>[] -> 'ok[] * 'error[]
+```
+
+Separates an array of `Result` values into a tuple of the `Ok` values and the `Error` values, preserving order within each group.
+
+## Examples
+
+### Example 1
+
+```fsharp
+let results = [| Ok 1; Error "bad"; Ok 2; Ok 3; Error "worse" |]
+
+results |> Array.partitionResults
+// ([| 1; 2; 3 |], [| "bad"; "worse" |])
+```
+
+### Example 2
+
+```fsharp
+// string -> Result<int, string>
+let tryParseInt str =
+  match System.Int32.TryParse str with
+  | true, x -> Ok x
+  | false, _ -> Error (sprintf "unable to parse '%s' to integer" str)
+
+[| "1"; "foo"; "3"; "bar" |]
+|> Array.map tryParseInt
+|> Array.partitionResults
+// ([| 1; 3 |], [| "unable to parse 'foo' to integer"; "unable to parse 'bar' to integer" |])
+```
+
+### Example 3
+
+All Ok values:
+
+```fsharp
+[| Ok 1; Ok 2; Ok 3 |] |> Array.partitionResults
+// ([| 1; 2; 3 |], [||])
+```
+
+All Error values:
+
+```fsharp
+[| Error "a"; Error "b" |] |> Array.partitionResults
+// ([||], [| "a"; "b" |])
+```

gitbook/list/partitionResults.md

@@ -0,0 +1,53 @@
+# List.partitionResults
+
+Namespace: `FsToolkit.ErrorHandling`
+
+## Function Signature
+
+```fsharp
+Result<'ok, 'error> list -> 'ok list * 'error list
+```
+
+Separates a list of `Result` values into a tuple of the `Ok` values and the `Error` values, preserving order within each group.
+
+## Examples
+
+### Example 1
+
+```fsharp
+let results = [Ok 1; Error "bad"; Ok 2; Ok 3; Error "worse"]
+
+results |> List.partitionResults
+// ([1; 2; 3], ["bad"; "worse"])
+```
+
+### Example 2
+
+```fsharp
+// string -> Result<int, string>
+let tryParseInt str =
+  match System.Int32.TryParse str with
+  | true, x -> Ok x
+  | false, _ -> Error (sprintf "unable to parse '%s' to integer" str)
+
+["1"; "foo"; "3"; "bar"]
+|> List.map tryParseInt
+|> List.partitionResults
+// ([1; 3], ["unable to parse 'foo' to integer"; "unable to parse 'bar' to integer"])
+```
+
+### Example 3
+
+All Ok values:
+
+```fsharp
+[Ok 1; Ok 2; Ok 3] |> List.partitionResults
+// ([1; 2; 3], [])
+```
+
+All Error values:
+
+```fsharp
+[Error "a"; Error "b"] |> List.partitionResults
+// ([], ["a"; "b"])
+```

gitbook/seq/partitionResults.md

@@ -0,0 +1,55 @@
+# Seq.partitionResults
+
+Namespace: `FsToolkit.ErrorHandling`
+
+## Function Signature
+
+```fsharp
+seq<Result<'ok, 'error>> -> 'ok[] * 'error[]
+```
+
+Separates a sequence of `Result` values into a tuple of the `Ok` values and the `Error` values as arrays, preserving order within each group.
+
+See also [Array.partitionResults](../array/partitionResults.md).
+
+## Examples
+
+### Example 1
+
+```fsharp
+let results = seq { Ok 1; Error "bad"; Ok 2; Ok 3; Error "worse" }
+
+results |> Seq.partitionResults
+// ([| 1; 2; 3 |], [| "bad"; "worse" |])
+```
+
+### Example 2
+
+```fsharp
+// string -> Result<int, string>
+let tryParseInt str =
+  match System.Int32.TryParse str with
+  | true, x -> Ok x
+  | false, _ -> Error $"unable to parse '{str}' to integer"
+
+["1"; "foo"; "3"; "bar"]
+|> Seq.map tryParseInt
+|> Seq.partitionResults
+// ([| 1; 3 |], [| "unable to parse 'foo' to integer"; "unable to parse 'bar' to integer" |])
+```
+
+### Example 3
+
+All Ok values:
+
+```fsharp
+seq { Ok 1; Ok 2; Ok 3 } |> Seq.partitionResults
+// ([| 1; 2; 3 |], [||])
+```
+
+All Error values:
+
+```fsharp
+seq { Error "a"; Error "b" } |> Seq.partitionResults
+// ([||], [| "a"; "b" |])
+```

src/FsToolkit.ErrorHandling/Array.fs

@@ -233,3 +233,22 @@ module Array =
     let sequenceVOptionM xs = traverseVOptionM id xs
 
 #endif
+
+    /// <summary>
+    /// Partitions an array of results into a tuple of the ok values and the error values.
+    /// </summary>
+    /// <param name="input">The input array of results.</param>
+    /// <returns>A tuple where the first element is an array of all Ok values and the second is an array of all Error values.</returns>
+    let partitionResults (input: Result<'ok, 'error>[]) : 'ok[] * 'error[] =
+        if System.Object.ReferenceEquals(input, null) then
+            nullArg (nameof input)
+
+        let oks = ResizeArray()
+        let errors = ResizeArray()
+
+        for x in input do
+            match x with
+            | Ok v -> oks.Add v
+            | Error e -> errors.Add e
+
+        oks.ToArray(), errors.ToArray()

src/FsToolkit.ErrorHandling/List.fs

@@ -274,3 +274,22 @@ module List =
 
 
 #endif
+
+    /// <summary>
+    /// Partitions a list of results into a tuple of the ok values and the error values.
+    /// </summary>
+    /// <param name="input">The input list of results.</param>
+    /// <returns>A tuple where the first element is a list of all Ok values and the second is a list of all Error values.</returns>
+    let partitionResults (input: Result<'ok, 'error> list) : 'ok list * 'error list =
+        if System.Object.ReferenceEquals(input, null) then
+            nullArg (nameof input)
+
+        let oks = ResizeArray()
+        let errors = ResizeArray()
+
+        for x in input do
+            match x with
+            | Ok v -> oks.Add v
+            | Error e -> errors.Add e
+
+        List.ofSeq oks, List.ofSeq errors

src/FsToolkit.ErrorHandling/Seq.fs

@@ -501,3 +501,22 @@ let traverseVOptionM f xs =
 let sequenceVOptionM xs = traverseVOptionM id xs
 
 #endif
+
+/// <summary>
+/// Partitions a sequence of results into a tuple of the ok values and the error values.
+/// </summary>
+/// <param name="input">The input sequence of results.</param>
+/// <returns>A tuple where the first element is an array of all Ok values and the second is an array of all Error values.</returns>
+let partitionResults (input: SeqNull<Result<'ok, 'error>>) : 'ok[] * 'error[] =
+    if isNull input then
+        nullArg (nameof input)
+
+    let oks = ResizeArray()
+    let errors = ResizeArray()
+
+    for x in input do
+        match x with
+        | Ok v -> oks.Add v
+        | Error e -> errors.Add e
+
+    oks.ToArray(), errors.ToArray()