[swift-evolution] Proposal: Filter split extension on Sequence to return tuple of sequences that meet criteria and that do not

[gadiraju praneeth]

I added an extension to do this, something like this:

extension Array {

    func filterSplit(includeElement: (Element) -> Bool) -> ([Element],
[Element]) {

        var elementsSatisfyingCondition = [Element]()

        var elementsNotSatisfyingCondition = [Element]()



        self.forEach { element in

            if includeElement(element)
{ elementsSatisfyingCondition.append(element) }

            else { elementsNotSatisfyingCondition.append(element) }

        }



        return (elementsSatisfyingCondition, elementsNotSatisfyingCondition)

    }

}


that way you can right away do: values.filterSplit { <yourPredicateBlock> }



On Wed, Jun 8, 2016 at 3:40 PM, Dave Abrahams via swift-evolution <
swift-evolution at swift.org> wrote:

>
> on Wed Jun 08 2016, Dave Abrahams <swift-evolution at swift.org> wrote:
>
> > on Wed Jun 08 2016, gadiraju praneeth <swift-evolution at swift.org> wrote:
> >
> >> Many times, I came across a scenario where I had to filter an array
> with a
> >> condition and filter the same array with opposite of that condition. For
> >> example:
> >>
> >> let values = [2, 4, 3, 5, 6, 9]
> >>
> >> let divisibleByTwo = values.filter { $0 % 2 == 0 }
> >> let notDivisibleByTwo = values.filter { $0 % 2 != 0 }
> >>
> >> Is there a way currently where we can filter the array into two arrays
> >> based on a condition?
> >
> > Well, you need a stable partition for this if you care about ordering
> > (see
> >
> https://github.com/apple/swift/blob/master/test/Prototypes/Algorithms.swift#L299
> )
> > but then you can do
> >
> > var parts = values
> > let mid = values.stablePartition { $0 % 2 == 0 }
> > let divisibleByTwo = parts.prefix(upTo: mid)
> > let notDivisibleByTwo = parts.suffix(from: mid)
> >
> > Nate Cook has an enhancement to the result of stablyPartitioned in that
> > prototype that would let you write:
> >
> >   let parts = values.stablyPartitioned { $0 % 2 == 0 }
> >   let divisibleByTwo = parts.prefix(upTo: parts.partitionPoint)
> >   let notDivisibleByTwo = parts.suffix(from: parts.partitionPoint)
>
> Hmm, come to think of it, Nate, maybe there should also be a more
> convenient way to get the two partitions from the result.
>
> --
> Dave
>
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