CODEWITHSUNDEEP
swiftdictionarynsdate
jdejde
jdejde

Reputation: 45

How to sort a dictionary in Swift by NSDate?

I have a dictionary in Swift that looks somewhat like this:

[
  "1": [
    "start": //An NSDate,
    "end": //An NSDate,
    "id": "1",
    "other non relevant items": "below",
  ]
]

And I want to sort it by the start date, with the key "start". I've seen the article on sorting dictionaries by value here but how would I do this with NSDates? Could you also give an example?

Upvotes: 2

Views: 1634

Answers (1)

Airspeed Velocity
Airspeed Velocity

Reputation: 40963

Note, you cannot sort a dictionary, except in the sense that you can sort any sequence, which turns it into an array of key/value pairs.

You haven’t said, but assuming your dictionary is of type [String:[String:AnyObject]], you could sort it (to get a result of an array of pairs, i.e. [(String,[String:AnyObject])]) like this:

let sorted = d.sort { lhs,rhs in
    let l = lhs.1["start"] as? NSDate
    let r = rhs.1["start"] as? NSDate
    return l < r
}

This is assuming you’ve also enhanced NSDate to have a < operator like so:

extension NSDate: Comparable { }

public func ==(lhs: NSDate, rhs: NSDate) -> Bool {
    return lhs.isEqualToDate(rhs)
}

public func <(lhs: NSDate, rhs: NSDate) -> Bool {
    return lhs.compare(rhs) == .OrderedAscending
}

Depending on what the actual type of your dictionary is, this might need some more type coercion.

If you don’t want the key in the sorted array (since it’s just a dupe of the ID), just sort the values:

let sorted = d.values.sort { lhs, rhs in
    let l = lhs["start"] as? NSDate
    let r = rhs["start"] as? NSDate
    return l < r
}

That said, I’d suggest instead of using a dictionary for anything more than the most basic of manipulation, that instead you write a custom struct and stash your data in that, this will make operations like this much simpler.

Upvotes: 3

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