A Swift extension to perform two filters simultaneously.

SequenceType+Multifilter.swift

extension SequenceType {
    /**
     Filter a single sequence into two "buckets", each an array containing objects of this collection's element type.
     - parameter includeElementInFirstCollection: A method that returns true for elements to include in the first collection.
     - parameter includeElementInSecondCollection: A method that returns true for elements to include in the second collection.
     - returns: A tuple of two arrays containing the elements in their respective buckets.
     */
    @warn_unused_result
    public func multifilter(@noescape includeInFirst includeElementInFirstCollection: (Self.Generator.Element) throws -> Bool, @noescape includeInSecond includeElementInSecondCollection: (Self.Generator.Element) throws -> Bool) rethrows -> ([Self.Generator.Element], [Self.Generator.Element]) {
        var firstCollection: [Self.Generator.Element] = []
        var secondCollection: [Self.Generator.Element] = []

        for element in self {
            if try includeElementInFirstCollection(element) {
                firstCollection.append(element)
            }

            if try includeElementInSecondCollection(element) {
                secondCollection.append(element)
            }
        }

        return (first: firstCollection, second: secondCollection)
    }
}