Sorting object array by both string date and boolean IOS

Question

I am trying to sort an array of objects that has a string date field in the from of "MM-DD-YYYY" and a boolean field. I want to create a function that sorts the array by both the date field and by the boolean field. I am having a hard time figuring out how to do this. The done field is default set to false and is not needed in my init func.

var items = [BucketItem(title: "blah", des: "description", lat: 134.6, lon: 27.0, dat: "02-14-2017"),BucketItem(title: "blah", des: "description", lat: 134.6, lon: 27.0, dat: "02-11-2017"), BucketItem(title: "blah blah", des: "description", lat: 134.6, lon: 27.0, dat: "02-9-2017")]

I looked at the .sort function but I don't how to compare the dates since they are in string format and I also don't know how to sort by two fields rather than just one. I want to sort so that if the boolean is true, then it is automatically less then an item with a boolean field of false. If both booleans are false, then it is sorted by date.

Answer 1

I would create an internal extension of Date that defines an initializer that takes a string, and parses it into a Date. You can use this in your entire module to parse dates according to your project's choice of date string format.

import Foundation

internal extension Date {
    init(_ s: String) {
        let df = DateFormatter()
        df.dateFormat = "MM-d-yyyy"
        guard let date = df.date(from: s) else {
            fatalError("Invalid date string.")
        }
        self.init(timeIntervalSince1970: date.timeIntervalSince1970)
    }
}

Then I would modify your structure to store the Date, rather than the String. Of course, modify the initializer to match.

let items = [
    BucketItem(
        title: "blah",
        des: "description",
        lat: 134.6, lon: 27.0,
        date: Date("02-14-2017")
    ),
    BucketItem(
        title: "blah",
        des: "description",
        lat: 134.6, lon: 27.0,
        date: Date("02-11-2017")
    ),
    BucketItem(
        title: "blah blah",
        des: "description",
        lat: 134.6, lon: 27.0,
        date: Date("02-9-2017")
]

From here, you have Comparable Date instances that you can use in your sorting. To see how to sort based off multiple criteria, see my answer here. Here's the rough code:

extension BucketItem: Equatable {
    static func ==(lhs: BucketItem, rhs: BucketItem) -> Bool {
        return lhs.isDone == rhs.isDone
            && lhs.date == rhs.date
            // && lhs.foo == rhs.foo
            // ...and so on, for all criteria that define equality of two BucketItems
    }
}

func <(lhs: Bool, rhs: Bool) -> Bool {
    return !lhs && rhs // false is less than true
}

extension BucketItem: Comparable {
    static func <(lhs: BucketItem, rhs: BucketItem) -> Bool {
        // First sort by isDone
        if (lhs.isDone != rhs.isDone) { return lhs.isDone < rhs.isDone }
        // else if (lhs.foo != rhs.foo) { return lhs.foo < rhs.foo }
        // ...and so on, for all sort criteria
        else (lhs.date != rhs.date) { return lhs.date < rhs.date }
    } 
}

letsortedItems = items.sorted()

Answer 2

You can define your BucketItem as

struct BucketItem {
let title: String
let des: String
let lat: Double
let lon: Double
let dat: String
let someBoolValue : Bool
var date: NSDate {
    get {
        return BucketItem.dateFormatter.dateFromString(dat)!
    }
}
static let dateFormatter: NSDateFormatter = {
    let formatter = NSDateFormatter()
    formatter.dateFormat = "MM-dd-yyyy"
    return formatter
    }()

}

Then call sort method on the array

 var items = [BucketItem(title: "blah", des: "description", lat: 134.6, lon: 27.0, dat: "02-14-2017", someBoolValue: false),BucketItem(title: "blah", des: "description", lat: 134.6, lon: 27.0, dat: "02-11-2017", someBoolValue :true), BucketItem(title: "blah blah", des: "description", lat: 134.6, lon: 27.0, dat: "02-9-2017",someBoolValue: false),  BucketItem(title: "blah blah", des: "description", lat: 134.6, lon: 27.0, dat: "02-9-2017",someBoolValue: true)]
    items.sortInPlace{
        if $0.date != $1.date {
            return $0.date.compare($1.date) == NSComparisonResult.OrderedAscending
        }
        else {
            return !$0.someBoolValue && $1.someBoolValue
        }
    }