Performs filter on a sectioned array

SectionedArrayFiltering.swift

struct SectionedArrayFiltering<T> {
    struct Result {
        let filteredSection: [Int]
        let filteredItemsBySection: [Int:[T]]
    }
    
    let input: [[T]]
    
    func filter(
        sectionFilter: (Int) -> Bool = {_ in true},
        itemFilter: (T) -> Bool
    ) -> Result {
        var includedSections = [Int]()
        var includedItemsBySection = [Int:[T]]()
        
        
        var section = 0
        for items in input {
            if !sectionFilter(section) {
                section += 1
                continue
            }
            for item in items {
                if itemFilter(item) {
                    var arr = includedItemsBySection[section] ?? []
                    arr.reserveCapacity(items.count)
                    arr.append(item)
                    includedItemsBySection[section] = arr
                }
            }
            if includedItemsBySection[section] != nil {
                includedSections.append(section)
            }
            section += 1
        }
        
        #if SectionedArrayFiltering_DEBUG
        print("SectionedArrayFiltering:", "Included Sections", includedSections)
        print("SectionedArrayFiltering:", "Included Items By Section", includedItemsBySection)
        #endif
        
        return Result(
            filteredSection: includedSections,
            filteredItemsBySection: includedItemsBySection
        )
    }
}