Swift Collection extensions

Collection extensions.swift

extension Array where Iterator.Element == CGFloat {
    var average: CGFloat? {
        guard !isEmpty else {
            return nil
        }
        
        var ret = self.reduce(CGFloat(0)) { (cur, next) -> CGFloat in
            var cur = cur
            cur += next
            return cur
        }
        let fcount = CGFloat(count)
        ret /= fcount
        return ret
    }
}

extension Array where Iterator.Element == SCNVector3 {
    var average: SCNVector3? {
        guard !isEmpty else {
            return nil
        }
        
        var ret = self.reduce(SCNVector3Zero) { (cur, next) -> SCNVector3 in
            var cur = cur
            cur.x += next.x
            cur.y += next.y
            cur.z += next.z
            return cur
        }
        let fcount = Float(count)
        ret.x /= fcount
        ret.y /= fcount
        ret.z /= fcount
        
        return ret
    }
}

extension Array where Iterator.Element == SCNMatrix4 {
    var average: SCNMatrix4? {
        guard !isEmpty else {
            return nil
        }
        
        var ret = self.reduce(SCNMatrix4()) { (cur, next) -> SCNMatrix4 in
            var cur = cur
            cur.m11 += next.m11
            cur.m12 += next.m12
            cur.m13 += next.m13
            cur.m14 += next.m14
            cur.m21 += next.m21
            cur.m22 += next.m22
            cur.m23 += next.m23
            cur.m24 += next.m24
            cur.m31 += next.m31
            cur.m32 += next.m32
            cur.m33 += next.m33
            cur.m34 += next.m34
            cur.m41 += next.m41
            cur.m42 += next.m42
            cur.m43 += next.m43
            cur.m44 += next.m44
            return cur
        }
        let fcount = Float(count)
        ret.m11 /= fcount
        ret.m12 /= fcount
        ret.m13 /= fcount
        ret.m14 /= fcount
        ret.m21 /= fcount
        ret.m22 /= fcount
        ret.m23 /= fcount
        ret.m24 /= fcount
        ret.m31 /= fcount
        ret.m32 /= fcount
        ret.m33 /= fcount
        ret.m34 /= fcount
        ret.m41 /= fcount
        ret.m42 /= fcount
        ret.m43 /= fcount
        ret.m44 /= fcount
        
        return ret
    }
}


extension RangeReplaceableCollection where IndexDistance == Int {
    mutating func keepLast(_ elementsToKeep: Int) {
        if count > elementsToKeep {
            self.removeFirst(count - elementsToKeep)
        }
    }
}