Convert an array to matrix to find adjacent elements iOS swift

Codecracker
January 26, 2022
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1 vote
2 Answers

Convert this below array into matrix
Array

let ptsArray = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]

Matrix

    0    1   2   3   4   5
    6    7   8   9   10  11
    12   13  14  15  16  17

To find adjacent points in uniderectional like an below image

Expected output

(0,1) (0,6)
(1,2) (1,7)
(2,3) (2,8)
(3,4) (3,9)
(4,5) (4,10)
(5,11)

(6,7)  (6,12)
(7,8)  (7,13)
(8,9)  (8,14)
(9,10) (9,15)
(10,11) (10,16)
(11,17)

(12,13) 
(13,14)
(14,15)
(15,16)
(16,17)

My failed approach

 for i in 0..<pointsArray.count-1{
        if (i+1)%6 == 0 && i != 0{
            print("Connection ((i),(i+6))")
            nodesArray[i].addConnection(to: nodesArray[i+6], bidirectional: true, weight: 1)
        }
        if i>=pointsArray.count-6{
            print("Connection ((i),(i+1))")
            nodesArray[i].addConnection(to: nodesArray[i+1], bidirectional: true, weight: 1)
        }
        else{
            print("Connection ((i),(i+1)) ((i),(i+6))")
            nodesArray[i].addConnection(to: nodesArray[i+1], bidirectional: true, weight: 1)
            nodesArray[i].addConnection(to: nodesArray[i+6], bidirectional: true, weight: 1)
        }
    }

Output:

Connection (0,1) (0,6)
Connection (1,2) (1,7)
Connection (2,3) (2,8)
Connection (3,4) (3,9)
Connection (4,5) (4,10)
Connection (5,11)
Connection (5,6) (5,11)
Connection (6,7) (6,12)
Connection (7,8) (7,13)
Connection (8,9) (8,14)
Connection (9,10) (9,15)
Connection (10,11) (10,16)
Connection (11,17)
Connection (11,12) (11,17)
Connection (12,13)
Connection (13,14)
Connection (14,15)
Connection (15,16)
Connection (16,17)

Answers

In the desired output, I guess that it’s missing (9,15), (10,11), (10,16) and that (10,15) isn’t valid.

If we think about your desired output, we notice something.
Let’s name width = 6, it’s the "width" of your matrix.

We see the pattern:
(value, value + 1), (value, value + width)
With some excluded tests: does (value + width) exists ? And we are not at the end of the width.

Let’s, with a little reduce method:

let ptsArray = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]

let width = 6
let tuples = ptsArray.indices.reduce(into: [(Int, Int)]()) { partialResult, anIndex in
    if ptsArray.count > anIndex.advanced(by: 1) && anIndex % width != width - 1 {
        let newValue = (ptsArray[anIndex], ptsArray[anIndex.advanced(by: 1)])
        print(newValue)
        partialResult.append(newValue)
    }
    if ptsArray.count > anIndex.advanced(by: width) {
        let newValue = (ptsArray[anIndex], ptsArray[anIndex.advanced(by: width)])
        print(newValue)
        partialResult.append(newValue)
    }
    return
}
print(tuples)

I used "index", because in fact, points are in order here, but it could be any value, no? So let’s use the index instead.

So, with something a little more generic:

extension Array {
    func coupling(with width: Int) -> [(Element, Element)] {
        let couples = indices.reduce(into: [(Element, Element)]()) { partialResult, anIndex in
            if count > anIndex.advanced(by: 1) && anIndex % width != width - 1 {
                let newValue = (self[anIndex], self[anIndex.advanced(by: 1)])
                partialResult.append(newValue)
            }
            if count > anIndex.advanced(by: width) {
                let newValue = (self[anIndex], self[anIndex.advanced(by: width)])
                partialResult.append(newValue)
            }
            return
        }
        return couples
    }
}

Use:

let ptsArray = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]
let tuples2 = ptsArray. coupling(with: width)
print(tuples2)

let lettersArray = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P", "Q", "R"]
let tuples3 = lettersArray. coupling(with: width)
print(tuples3)

Another approach – convert your ptsArray into a 2-D matrix:

var matrix: [[Int]] = []

let numCols: Int = 6
var numRows: Int = 0

let ptsArray: [Int] = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]
    
for i in stride(from: 0, to: ptsArray.count, by: numCols) {
    // make sure we don't exceed the array limit
    if ptsArray.count >= i+numCols {
        matrix.append(Array(ptsArray[i..<i+numCols]))
    }
}

numRows = matrix.count

You can now get the right and down values (if they exist) like this:

func getPair2D(_ n: Int) -> (Int?, Int?) {
    
    let thisRow = n / numCols
    let thisCol = n % numCols
    
    let numToRight = thisCol < numCols-1 ? matrix[thisRow][thisCol+1] : nil
    let numToDown = thisRow < numRows-1 ? matrix[thisRow+1][thisCol] : nil
    
    return (numToRight, numToDown)
    
}

and this will print out the results:

for i in 0..<ptsArray.count {
        
    let (n1, n2) = getPair2D(i)
    var str = ""
    if let n1 = n1 {
        str += "((i), (n1))"
    }
    if let n2 = n2 {
        if !str.isEmpty { str += " " }
        str += "((i), (n2))"
    }

    print(str)
        
}

Here’s a simple view controller that let’s you tap any number to show the "right and down" matches:

class MatrixVC: UIViewController {
    
    var matrix: [[Int]] = []

    var views: [UIView] = []
    
    let numCols: Int = 6
    var numRows: Int = 0

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let ptsArray: [Int] = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]

        for i in stride(from: 0, to: ptsArray.count, by: numCols) {
            if ptsArray.count >= i+numCols {
                matrix.append(Array(ptsArray[i..<i+numCols]))
            }
        }
        
        numRows = matrix.count
        
        let oStack: UIStackView = {
            let v = UIStackView()
            v.axis = .vertical
            v.distribution = .fillEqually
            v.spacing = 2
            return v
        }()
        
        var n = 0
        for r in 0..<numRows {
            let rStack: UIStackView = {
                let v = UIStackView()
                v.axis = .horizontal
                v.distribution = .fillEqually
                v.spacing = 2
                return v
            }()
            for c in 0..<numCols {
                let v = UILabel()
                v.textAlignment = .center
                v.text = "(ptsArray[n])"
                v.isUserInteractionEnabled = true
                let t = UITapGestureRecognizer(target: self, action: #selector(gotTap(_:)))
                v.addGestureRecognizer(t)
                rStack.addArrangedSubview(v)
                views.append(v)
                if c < numCols-1 {
                    let iv = UIImageView(image: UIImage(systemName: "arrow.right"))
                    rStack.addArrangedSubview(iv)
                }
                n += 1
            }
            oStack.addArrangedSubview(rStack)
            if r < numRows-1 {
                let rStack: UIStackView = {
                    let v = UIStackView()
                    v.axis = .horizontal
                    v.distribution = .fillEqually
                    v.spacing = 2
                    return v
                }()
                for c in 0..<numCols {
                    let iv = UIImageView(image: UIImage(systemName: "arrow.down"))
                    rStack.addArrangedSubview(iv)
                    if c < numCols-1 {
                        let v = UIView()
                        rStack.addArrangedSubview(v)
                    }
                }
                oStack.addArrangedSubview(rStack)
            }
        }
    
        oStack.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(oStack)

        let g = view.safeAreaLayoutGuide
        NSLayoutConstraint.activate([
            
            oStack.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 40.0),
            oStack.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -40.0),
            oStack.centerXAnchor.constraint(equalTo: g.centerXAnchor),
            oStack.centerYAnchor.constraint(equalTo: g.centerYAnchor),
            
        ])

    }
    
    @objc func gotTap(_ g: UITapGestureRecognizer) {
        
        guard let v = g.view as? UILabel,
              let t = v.text,
              let n = Int(t)
        else { return }
        
        // if the tapped label is yellow, let's just deselect all
        let deselecting: Bool = views[n].backgroundColor == .yellow
        
        views.forEach { $0.backgroundColor = .clear }

        if deselecting {
            return()
        }
        
        views[n].backgroundColor = .yellow
        
        let (n1, n2) = getPair2D(n)
        if let n1 = n1 {
            views[n1].backgroundColor = .yellow
        }
        if let n2 = n2 {
            views[n2].backgroundColor = .yellow
        }

    }

    func getPair2D(_ n: Int) -> (Int?, Int?) {
        
        let thisRow = n / numCols
        let thisCol = n % numCols
        
        let numToRight = thisCol < numCols-1 ? matrix[thisRow][thisCol+1] : nil
        let numToDown = thisRow < numRows-1 ? matrix[thisRow+1][thisCol] : nil
        
        return (numToRight, numToDown)
        
    }
    
}