How to sort a Dictionary in Swift

Question

How can I sort a dictionary in Swift?

My Dictionary declaration:

var colorDictionary = Dictionary<Pixel, Int>() //pixel class stores RGB values of a pixel, Int stores the appearing times of the same color showing on the same image.

My target: I need the elements in the dictionary sorted by value (appearing times of colors) from high to low.

What I tried: I have done some research online, and I know the Dictionary in swift doesn't provide the sort function. So I wrote the following code:

 var tempArray = Array(colorDictionary.keys)

        var sortedKeys: () = sort(&tempArray){
            var obj1 = self.colorDictionary[$0]
            var obj2 = self.colorDictionary[$1]
            return obj1>obj2
        }



        println("the most color: \(colorDictionary[tempArray[0])")

Output I got: "the most color: Optional(27)" //where 27 is the highest appearing time of the color, which is the value of the dictionary.

Question: How could I make it return the key as well?

My Pixel Class:

//for making the hashvalue stuff equatable
func ==(lhs: Pixel, rhs: Pixel) -> Bool {
    return lhs.hashValue == rhs.hashValue
}

//customized class for storing pixel info of an image
class Pixel: Hashable  {
    //RGB components from one pixel
    let  r: CGFloat
    let  g: CGFloat
    let  b: CGFloat

    var  y: CGFloat = 0
    var  u: CGFloat = 0
    var  v: CGFloat = 0

    var theUIColorOfThisPixel:UIColor

    //adding for make the key hashable
    var hashValue: Int {
        return theUIColorOfThisPixel.hashValue
    }

    init(_thePixel: UIColor){
            r = _thePixel.components.red
            g = _thePixel.components.green
            b = _thePixel.components.blue


        theUIColorOfThisPixel=UIColor(red: r, green: g, blue: b, alpha: 1)
        rgbToYuv(r, _g: g, _b: b)



    }
}

[Problem solved] My solution: if I convert the result to Int (e.g. Int(colorDictionary[tempArray[0]]), it will just return the appearing time of the most common color on the image. For getting the UIColor of the pixel, I used:

var theMostUIColor: UIColor = tempArray[0].theUIColorOfThisPixel

I thought after storing my dictionary to the Array, it will just store the values. But now I found it actually stores the keys as well. Thanks for all the people who replied on this post. I appreciate!

possible duplicate of [Sort Dictionary by values in Swift](http://stackoverflow.com/questions/24090016/sort-dictionary-by-values-in-swift) — Eric Aya, Jul 10 '15 at 09:24
Hi Eric. Thanks for your reply. I tried this. However, it was not very easy to understand for me. some of the key was not defined when I copied them to my code. I had to change to other similar ways. That post did help me on some way, though. — Ares Li, Jul 10 '15 at 09:42

score 0 · Answer 1 · answered Jul 10 '15 at 09:22

You can return an array of tuples. Where each tuple has two values; the Pixel and the integer.

See: https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Functions.html#//apple_ref/doc/uid/TP40014097-CH10-ID164

How to sort a Dictionary in Swift

1 Answers1