Correct Observable.filteri bug and optimise Observable.mapi

paket.dependencies

@@ -3,12 +3,13 @@ source http://nuget.org/api/v2
 nuget FAKE
 nuget SourceLink.Fake
 nuget Nuget.CommandLine
-nuget FSharp.Core ~> 3.1.2
+nuget FSharp.Core ~> 4.0.0.1
 nuget Rx-Experimental ~> 2.2.5
 nuget Rx-Main ~> 2.2.5
 nuget Rx-PlatformServices ~> 2.2.5
 nuget Rx-Testing ~> 2.2.5
 nuget NUnit 
 nuget NUnit.Runners 
+nuget FsCheck.NUnit
 nuget FSharp.Formatting
 nuget FSharp.Compiler.Service

paket.lock

@@ -1,15 +1,21 @@
 NUGET
-  remote: http://nuget.org/api/v2
+  remote: http://www.nuget.org/api/v2
   specs:
-    FAKE (4.0.3)
-    FSharp.Compiler.Service (1.4.0.1)
-    FSharp.Core (3.1.2.5)
+    FAKE (4.12.2)
+    FsCheck (2.2.4)
+      FSharp.Core (>= 3.1.2.5)
+    FsCheck.Nunit (2.2.4)
+      FsCheck (>= 2.2.4)
+      NUnit (>= 2.6.4 < 2.7.0)
+      NUnit.Runners (>= 2.6.4 < 2.7.0)
+    FSharp.Compiler.Service (2.0.0.2)
+    FSharp.Core (4.0.0.1)
     FSharp.Formatting (2.10.0)
       FSharp.Compiler.Service (>= 0.0.87)
       FSharpVSPowerTools.Core (1.8.0)
     FSharpVSPowerTools.Core (1.8.0)
       FSharp.Compiler.Service (>= 0.0.87)
-    NuGet.CommandLine (2.8.6)
+    NuGet.CommandLine (3.3.0)
     NUnit (2.6.4)
     NUnit.Runners (2.6.4)
     Rx-Core (2.2.5)
@@ -35,4 +41,4 @@ NUGET
       Rx-Main (>= 2.2.5)
     Rx-Testing (2.2.5)
       Rx-Main (>= 2.2.5)
-    SourceLink.Fake (1.0.0)
+    SourceLink.Fake (1.1.0)

src/Observable.fs

@@ -560,7 +560,7 @@ module Observable =
     /// Filters the observable elements of a sequence based on a predicate by 
     /// incorporating the element's index
     let filteri predicate (source: IObservable<'T>)  = 
-        Observable.Where( source, Func<_,_> predicate )
+        Observable.Where( source, Func<_,_,_> (fun i x -> predicate x i) )
 
 
     /// Invokes a specified action after the source observable sequence
@@ -1028,12 +1028,7 @@ module Observable =
     /// Maps the given observable with the given function and the 
     /// index of the element
     let mapi (f:int -> 'Source -> 'Result) (source:IObservable<'Source>) =
-        source
-        |> Observable.scan ( fun (i,_) x -> (i+1,Some(x))) (-1,None)
-        |> Observable.map
-            (   function
-                | i, Some(x) -> f i x
-                | _, None    -> invalidOp "Invalid state"   )
+        Observable.Select (source, Func<_,_,_> (fun i x -> f x i))
 
 
     /// Maps two observables to the specified function.

tests/FsCheckAddin.fs

@@ -0,0 +1,15 @@
+namespace FsCheck.NUnit.Examples
+
+open NUnit.Core.Extensibility
+
+open FsCheck.NUnit
+open FsCheck.NUnit.Addin
+
+[<NUnitAddin(Description = "FsCheck addin")>]
+type FsCheckAddin() =
+    interface IAddin with
+        override x.Install host =
+            let tcBuilder = new FsCheckTestCaseBuilder()
+            host.GetExtensionPoint("TestCaseBuilders").Install(tcBuilder)
+            true
+

tests/ObservableSpecs.fs

@@ -5,6 +5,7 @@ open System.Reactive.Linq
 open FSharp.Control.Reactive
 open Builders
 open NUnit.Framework
+open FsCheck.NUnit
 open Microsoft.Reactive.Testing
 open System.Reactive.Subjects
 open System.Reactive.Concurrency
@@ -550,4 +551,34 @@ let ``FlatMapAsync should take F# async workflows and flatmap them to observable
     Assert.That(result.Count, Is.EqualTo 3)
     Assert.That(result.[0], Is.EqualTo expected)
     Assert.That(result.[1], Is.EqualTo expected)
-    Assert.That(result.[2], Is.EqualTo expected)
+    Assert.That(result.[2], Is.EqualTo expected)
+
+[<Property>]
+let ``Observable.mapi should be equivalent to Array.mapi`` (items : int array) =
+    items
+    |> Observable.ofSeq
+    |> Observable.mapi (fun i x -> (i, x))
+    |> Observable.toEnumerable
+    |> Seq.toArray
+    |> (=) (items |> Array.mapi (fun i x -> (i, x)))
+
+[<Property>]
+let ``filteri should be equivalent to mapi then filter`` (items : int array) =
+    let predicate i x = (i % 2 = 0) && (x > 0)
+
+    let filtered =
+        items
+        |> Observable.ofSeq
+        |> Observable.mapi (fun i x -> (i, x))
+        |> Observable.filter (fun (i, x) -> predicate i x)
+        |> Observable.map snd
+        |> Observable.toEnumerable
+        |> Seq.toArray
+
+    let filtered' =
+        Observable.ofSeq items
+        |> Observable.filteri predicate
+        |> Observable.toEnumerable
+        |> Seq.toArray
+
+    filtered = filtered'

tests/paket.references

@@ -1,6 +1,7 @@
 FSharp.Core
 NUnit
 NUnit.Runners
+FsCheck.NUnit
 Rx-Core
 Rx-Experimental
 Rx-Interfaces