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Add TraverseFilter.mapAccumulateFilter #4561

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Add TraverseFilter.mapAccumulateFilter #4561

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021f5f8
Add TraverseFilter.mapAccumulateFilter
Masynchin Feb 19, 2024
17389c0
Add tests for TraverseFilter.mapAccumulateFilter
Masynchin Feb 19, 2024
23fa3db
Optimize mapAccumulateFilter for List
Masynchin Feb 19, 2024
8040c23
Optimize mapAccumulateFilter for Vector
Masynchin Feb 19, 2024
cb6d411
Optimize mapAccumulateFilter for Chain
Masynchin Feb 19, 2024
277593b
Optimize mapAccumulateFilter for Option
Masynchin Feb 19, 2024
15ec803
Fix formatting for TraverseFilter[Option].mapAccumulateFilter
Masynchin Feb 19, 2024
9adf4d5
Optimize mapAccumulateFilter for Queue
Masynchin Feb 19, 2024
a414be1
Optimize mapAccumulateFilter for ArraySeq
Masynchin Feb 19, 2024
35706a7
Run scalafmt
Masynchin Feb 19, 2024
778aad2
Add scaladoc for mapAccumulateFilter
Masynchin Apr 6, 2024
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5 changes: 5 additions & 0 deletions core/src/main/scala/cats/TraverseFilter.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -122,6 +122,9 @@ trait TraverseFilter[F[_]] extends FunctorFilter[F] {
override def mapFilter[A, B](fa: F[A])(f: A => Option[B]): F[B] =
traverseFilter[Id, A, B](fa)(f)

def mapAccumulateFilter[S, A, B](init: S, fa: F[A])(f: (S, A) => (S, Option[B])): (S, F[B]) =
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traverseFilter(fa)(a => State(s => f(s, a))).run(init).value
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Can we override this for some of the built in collections? State is rather slow so we should avoid it for List, Vector, Chain, NonEmptyList, NonEmptyVector, ...

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@Masynchin Masynchin Feb 19, 2024 •
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I can copy StaticMethods.mapAccumulateFromStrictFunctor for mapAccumulateFilter, this will cover for some collections


/**
* Removes duplicate elements from a list, keeping only the first occurrence.
*/
Expand Down Expand Up @@ -184,6 +187,8 @@ object TraverseFilter {
typeClassInstance.filterA[G, A](self)(f)(G)
def traverseEither[G[_], B, C](f: A => G[Either[C, B]])(g: (A, C) => G[Unit])(implicit G: Monad[G]): G[F[B]] =
typeClassInstance.traverseEither[G, A, B, C](self)(f)(g)(G)
def mapAccumulateFilter[S, B](init: S)(f: (S, A) => (S, Option[B])): (S, F[B]) =
typeClassInstance.mapAccumulateFilter[S, A, B](init, self)(f)
def ordDistinct(implicit O: Order[A]): F[A] = typeClassInstance.ordDistinct(self)
def hashDistinct(implicit H: Hash[A]): F[A] = typeClassInstance.hashDistinct(self)
}
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13 changes: 13 additions & 0 deletions tests/shared/src/test/scala/cats/tests/TraverseFilterSuite.scala
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Expand Up @@ -38,6 +38,19 @@ abstract class TraverseFilterSuite[F[_]: TraverseFilter](name: String)(implicit

implicit def T: Traverse[F] = implicitly[TraverseFilter[F]].traverse

test(s"TraverseFilter[$name].mapAccumulateFilter") {
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Looks like it does not check the default implementation (based on State), does it?
Except maybe one for Stream, but I wouldn't count on it.

For testing default implementations we usually use ListWrapper from testkit:
ListWrapper.scala

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I had straightforwardly copy-pasted and updated tests from mapAccumulate here:

cats/tests/shared/src/test/scala/cats/tests/TraverseSuite.scala

Lines 45 to 56 in 70dbf8f

test(s"Traverse[$name].mapAccumulate") {
forAll { (init: Int, fa: F[Int], fn: ((Int, Int)) => (Int, Int)) =>
val lhs = fa.mapAccumulate(init)((s, a) => fn((s, a)))
val rhs = fa.foldLeft((init, List.empty[Int])) { case ((s1, acc), a) =>
val (s2, b) = fn((s1, a))
(s2, b :: acc)
}
assert(lhs.map(_.toList) === rhs.map(_.reverse))
}
}

If that tests doesn't test default implementation too, I can update mapAccumulateFilter tests. Can you provide an example of how to pass ListWrapper?

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For testing default implementations we usually use ListWrapper from testkit: ListWrapper.scala

I am failing to understand how to use ListWrapper to test mapAccumulateFilter. I was looking for examples in other Suites, but it is either suites for data and not typeclasses (OptionT, Try, etc.), or it refers to <Typeclass>Tests[ListWrapper].<methodToTest>, like in the ApplicativeSuite:

cats/tests/shared/src/test/scala/cats/tests/ApplicativeSuite.scala

Lines 102 to 104 in 70dbf8f

implicit val listwrapperApplicative: Applicative[ListWrapper] = ListWrapper.applicative
implicit val listwrapperCoflatMap: CoflatMap[ListWrapper] = Applicative.coflatMap[ListWrapper]
checkAll("Applicative[ListWrapper].coflatMap", CoflatMapTests[ListWrapper].coflatMap[String, String, String])

which I can not apply here, because we don't have TraverseFilter[?].mapAccumulateFilter. Am I missing something?

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@satorg satorg Apr 10, 2024 •
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My apologies for the delay – I was snowed under a bit. Actually, there's TraverseFilter for ListWrapper:

cats/testkit/src/main/scala/cats/tests/ListWrapper.scala

Lines 80 to 90 in 47fbad7

val traverseFilter: TraverseFilter[ListWrapper] = {
val F = TraverseFilter[List]
new TraverseFilter[ListWrapper] {
def traverse = ListWrapper.traverse
def traverseFilter[G[_], A, B](
fa: ListWrapper[A]
)(f: A => G[Option[B]])(implicit G: Applicative[G]): G[ListWrapper[B]] =
G.map(F.traverseFilter(fa.list)(f))(ListWrapper.apply)
}
}

To test the default implementation you can either call it directly:

ListWrapper.traverseFilter.mapAccumulateFilter(...)

or make it an implicit in the scope:

implicit val listWrapperTraverseFilter: TraverseFilter[ListWrapper] = ListWrapper.traverseFilter

And then you can work with TraverseFilter for ListWrapper as usual.

forAll { (init: Int, fa: F[Int], fn: ((Int, Int)) => (Int, Option[Int])) =>
val lhs = fa.mapAccumulateFilter(init)((s, a) => fn((s, a)))

val rhs = fa.foldLeft((init, List.empty[Int])) { case ((s1, acc), a) =>
val (s2, b) = fn((s1, a))
(s2, b.fold(acc)(_ :: acc))
}

assert(lhs.map(_.toList) === rhs.map(_.reverse))
}
}

test(s"TraverseFilter[$name].ordDistinct") {
forAll { (fa: F[Int]) =>
fa.ordDistinct.toList === fa.toList.distinct
Expand Down