iOS Swift：将数组排序为多维数组

Question

I have an array of CKRecords. Each record has startTime and a Name , among other values. What I would like to do is sort the records first by unique startTime and then within each startTime sort by unique Name .

The end result would be an array that looks like this (I think): records = [Date: [Name: [CKRecord]]]

Here is what I have right now:

func buildIndex(records: [CKRecord]) -> [[CKRecord]] {
var dates = [NSDate]()
var result = [[CKRecord]]()

for record in records {
    var date = record.objectForKey("startTime") as! NSDate

    if !contains(dates, date) {
        dates.append(date)
    }
}

for date in dates {
    var recordForDate = [CKRecord]()

    for (index, exercise) in enumerate(exercises) {
        let created = exercise.objectForKey("startTime") as! NSDate

        if date == created {
            let record = exercises[index] as CKRecord
            recordForDate.append(record)
        }
    }
    result.append(recordForDate)
}

return result
}

let records = self.buildIndex(data)

Answer 1

Why not use sorted ? Like this.

// A simplified version of your `CKRecord` just for demonstration
struct Record {
    let time: NSDate
    let name: String
}

let records = [
    Record(time: NSDate(timeIntervalSince1970: 1), name: "a"),
    Record(time: NSDate(timeIntervalSince1970: 2), name: "b"),
    Record(time: NSDate(timeIntervalSince1970: 1), name: "c"),
    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]] {
    var g = [NSDate: [Record]]()
    for e in records {
        if (g[e.time] == nil) {
            g[e.time] = []
        }
        g[e.time]!.append(e) // grouping by `time`
    }
    return sorted(g.keys) { (a: NSDate, b: NSDate) in
        a.compare(b) == .OrderedAscending // sorting the outer array by 'time'
    }
    // sorting the inner arrays by `name`
    .map { sorted(g[$0]!) { $0.name < $1.name } } 
}

println(buildIndex(records))

Answer 2

First of all, you're not really trying to sort an array here, you're trying to order a dictionary, which isn't built to be iterated over sequentially. In fact even if you do sort the array first and then build the dictionary like this:

var sortedRecords = [NSDate: [String: CKRecord]]()
records.sort { return $0.date.timeIntervalSinceDate($1.date) < 0 }

for record in records {
    if sortedRecords[record.date] != nil {
        sortedRecords[record.date] = [String: CKRecord]()
    }

    sortedRecords[record.date]![record.name] = record
}

The order isn't guaranteed when you iterate over it in the future. That said, a dictionary is essentially a look up table, and elements can be accessed in O(log n) time. What you'll really want to do is either drop the dictionary is favor of an array of [CKRecord] and then sort like this:

records.sort { $0.date.timeIntervalSinceDate($1.date) == 0 ? $0.name < $1.name : $0.date.timeIntervalSinceDate($1.date) < 0 }

Or, depending on what your end goal is, iterate across a range of dates, plucking the entries from the dictionary as you go.

Answer 3

You could execute the CloudKit query and make sure that you get the array returned in the correct sort order like this:

    query.sortDescriptors = [NSSortDescriptor(key: "startTime", ascending: true), NSSortDescriptor(key: "Name", ascending: true)]

And then if you go to the detail view, you could use the filter for getting the records for that day like this:

   var details = records.filter { (%0.objectForKey("startTime") As! NSDate) == selectedDate }