group dispatch in swift 3

gistfile1.txt

let backgroundQ = DispatchQueue.global(attributes: .qosDefault)
let group = DispatchGroup()

var someData:[Data] = []
for number in 0..<n {
    group.enter()
    backgroundQ.async(group: group,  execute: {  
        if number > 50 {
            fill.append(number)
        }
        group.leave()

    })
}

group.notify(queue: DispatchQueue.main, execute: {
    print("All Done"); completion(result: fill)
})