Array#sortedGroupBy

so28789095.swift

struct Record {
    let time: NSDate
    let name: String
}

extension Array {
    func sortedGroupBy(isOrderedBefore: (T, T) -> Bool) -> [[T]] {
        let tmp = sorted(isOrderedBefore)
        var out = [[T]]()
        for (i, e) in enumerate(tmp) {
            if i > 0 && !(
                isOrderedBefore(tmp[i-1], e) ||
                isOrderedBefore(e, tmp[i-1]))
            {
                out[out.count - 1].append(e)
            }
            else {
                out.append([e])
            }
        }
        return out
    }
}

let records = [
    Record(time: NSDate(timeIntervalSince1970: 1), name: "a"),
    Record(time: NSDate(timeIntervalSince1970: 2), name: "b"),
    Record(time: NSDate(timeIntervalSince1970: 1), name: "a"),
    Record(time: NSDate(timeIntervalSince1970: 3), name: "d"),
    Record(time: NSDate(timeIntervalSince1970: 3), name: "e"),
    Record(time: NSDate(timeIntervalSince1970: 2), name: "f"),
]

func buildIndex(records: [Record]) -> [[[Record]]] {
    return records
        .sortedGroupBy { (a: Record, b: Record) in
            a.time.compare(b.time) == .OrderedAscending
        }
        .map {
            $0.sortedGroupBy { $0.name < $1.name }
        }
}