CODEWITHSUNDEEP
swift
user7531085
user7531085

Reputation:

Sorting arrays based on number of matches

I am trying to find the number of array item matches between multiple test arrays and one control array. After finding the number of matches, I want to append the test arrays to another array, sorted by number of matches between the control array and test array. For example, a test array with 3 matches would be at index 0, 2 matches at index 1, and so on.

let controlArray = ["milk", "honey"]
let test1 = ["honey", "water"]
let test2 = ["milk", "honey", "eggs"]
var sortedArrayBasedOnMatches = [[String]]()

/*I want to append test1 and test2 to sortedArrayBasedOnMatches based on how many items 
test1 and test2 have in common with controlArray*/

/*in my example above, I would want sortedArrayBasedOnMatches to equal 
[test2, test1] since test 2 has two matches and test 1 only has one*/

Upvotes: 0

Views: 140

Answers (3)

Jae Yang
Jae Yang

Reputation: 539

This will cover the case where elements are not unique in your control array(such as milk, milk, honey...) and with any number of test arrays. 

func sortedArrayBasedOnMatches(testArrays:[[String]], control: [String]) -> [[String]]{
var final = [[String]].init()
var controlDict:[String: Int] = [:]
var orderDict:[Int: [[String]]] = [:] // the value is a array of arrays because there could be arrays with the same amount of matches.
for el in control{
    if controlDict[el] == nil{
        controlDict[el] = 1
    }
    else{
        controlDict[el] = controlDict[el]! + 1
    }
}
for tArr in testArrays{
    var totalMatches = 0
    var tDict = controlDict
    for el in tArr{
        if tDict[el] != nil && tDict[el] != 0 {
            totalMatches += 1
            tDict[el] = tDict[el]! - 1
        }
    }
    if orderDict[totalMatches] == nil{
        orderDict[totalMatches] = [[String]].init()
    }
    orderDict[totalMatches]?.append(tArr)
}
for key in Array(orderDict.keys).sorted(by: >) {
    for arr in orderDict[key]! {
        final.append(arr)
    }
}
    return final
}

Upvotes: 0

Cristik
Cristik

Reputation: 32853

This can be done in a very functional and Swiftish way by writing a pipeline to process the input arrays:

let sortedArrayBasedOnMatches = [test1, test2] // initial unsorted array
    .map { arr in (arr, arr.filter { controlArray.contains($0) }.count) } // making pairs of (array, numberOfMatches)
    .sorted { $0.1 > $1.1 } // sorting by the number of matches
    .map { $0.0 } // getting rid of the match count, if not needed

Update As @Carpsen90 pointed out, Switf 5 comes with support for count(where:) which reduces the amount of code needed in the first map() call. A solution that makes use of this could be written along the lines of

// Swift 5 already has this, let's add it for current versions too
#if !swift(>=5)
extension Sequence {
    // taken from the SE proposal
    // https://github.com/apple/swift-evolution/blob/master/proposals/0220-count-where.md#detailed-design
    func count(where predicate: (Element) throws -> Bool) rethrows -> Int {
        var count = 0
        for element in self {
            if try predicate(element) {
                count += 1
            }
        }
        return count
    }
}
#endif

let sortedArrayBasedOnMatches = [test1, test2] // initial unsorted array
    .map { (arr: $0, matchCount: $0.count(where: controlArray.contains)) } // making pairs of (array, numberOfMatches)
    .sorted { $0.matchCount > $1.matchCount } // sorting by the number of matches
    .map { $0.arr } // getting rid of the match count, if not needed

Another change in style from the original solution is to use labels for the tuple components, this makes the code a little bit clearer, but also a little bit more verbose.

Upvotes: 3

rmaddy
rmaddy

Reputation: 318854

One option is to convert each array to a Set and find the count of elements in the intersection with controlArray.

let controlArray = ["milk", "honey"]
let test1 = ["honey", "water"]
let test2 = ["milk", "honey", "eggs"]
var sortedArrayBasedOnMatches = [ test1, test2 ].sorted { (arr1, arr2) -> Bool in
    return Set(arr1).intersection(controlArray).count > Set(arr2).intersection(controlArray).count
}
print(sortedArrayBasedOnMatches)

Upvotes: 0

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