I receive the data from websocket in every second and I want to take 8 of them in an array and send to the different endpoint, and when the first 8 items is added, I want to remove all items inside the array and fill with the new ones, here is my codes:
if dataArray.count <= 7 {
dataArray.append(value)
if dataArray.count == 8 {
self.sendData(data: dataArray)
dataArray.removeAll()
}
}
Just want to know that there is a better / safer way to do that?
Thank you so much
Your code is fine, if you are worry about condition race, maybe consider below
Make a copy array before sending:
let valuesToSend = dataArray
Replace old one with new array once reach 8 items:
dataArray = [Data]()
I'm not sure if you need the first comparison.
dataArray.append(value)
if dataArray.count == 7 {
sendData(data: dataArray)
dataArray.removeAll()
}
And since you want the first 8 elements, shouldn't you compare the count with 8?
Also, you might want to check what happens in a possible overflow case (count > 8).
Another approach would be using a switch case
dataArray.append(value)
switch dataArray.count {
case 8:
sendData(data: dataArray)
dataArray.removeAll()
case 9...:
fatalError("Should never happen")
default:
}
Related
I'm really new to Swift and I have a task asking me to create a while loop that simulates rolling a 6-sided dice repeatedly until a 1 is rolled. After each roll, print the value.
In just about every iteration I've tried over the last 2 hours I keep ending in an infinite loop that explodes Xcode.
Any help would be fantastic!
var dieRoll = Int.random(in: 1...6)
while dieRoll <= 6 {
print (dieRoll)
if dieRoll == 1 {
print ("You win!")
}
}
Got it to this point, it no longer runs endlessly but it acts weird and returns values of 1 without printing "You win!"
func dieRoll(x: Int) -> Int {
return Int.random(in:1...6)
}
while dieRoll(x: 0) > 1 {
print(dieRoll(x: 0))
if dieRoll(x: 1) == 1 {
print("You win!")
}
else {
RETURN
}
}
Your dieRoll variable is declared AS A VARIABLE yet you never change it! Try “rerolling” within the While Loop
Also, there’s always the chance that a 6 never gets rolled... idk if you want to mess with “real” probabilities but if you’re finding issues you may want to institute a “max number of rolls”... personally I wouldn’t but hey you never know
TDLR: last line of the while-loop should reroll your dieRoll var
Okay, so I got away from the string text and focused on what the code was saying versus what my typing was saying. Ended up with this (probably a monstrosity to you experienced folks) but it looks something like this.
var rolling = Int.random(in: 1...6)
while rolling > 1 {
print(rolling)
if rolling == 1 {
break
} else {
rolling = Int.random(in: 1...6)
}
}
print(rolling)
And every time I run it it ends on a 1 so it does what it needs to!
I need to fetch from Realm Results 20 objects or less. A database can be heavy, so Results.count is a long time for calling.
So, what I need is to fetch objects from Results one by one until I get 20 or until last object.
But, when I'm trying to fetch index after the last object it's throwing Realm exception 'Index x is out of bounds (must be less than x)'.
So, this one isn't working:
let searchResult = Ticket().get(filter: "base == nil && deleted == 0 AND orderPaidAt > 0 AND (\(query))").sorted(byKeyPath: "orderPaidAt")
for i in 0..<20 {
if let ticket = searchResult[i] as? Ticket {
...
} else {
break
}
}
If I'm trying to use searchResult.count or searchResult.endIndex it increases a time a lot, especially on old devices. That's why I want to avoid it.
The results are lazily loaded, so you could loop through the results one by one, until the end, or until you hit a self-set count:
let searchResult = Ticket().get(filter: "base == nil && deleted == 0 AND orderPaidAt > 0 AND (\(query))").sorted(byKeyPath: "orderPaidAt")
var count = 0
for thisTicket in searchResult {
// do something
count += 1
if count > 20 { break }
}
This way you are only loading the values that you need, and never calling count or accessing the results out of bounds.
You can use prefix(maxLenght: Int) method to get a subCollection with specified maxLenght.
Example:
realm.objects(ObjectModel.self).prefix(20).count
While this may not be a good example, but as the question states, I wish to compare randomNo to the sets within numberSets. However, the moment one number is found I want to know if there is a way to skip to the next set.
In summary randomNo contains 2 numbers which can be found in the same set these are "6" and "9". I want to know if the moment I find "6" and can void the rest of the set and move onto the next set without cycling through the rest of the numbers in the set
init() {
let numberSet1 : Set<Int> = [1,2,3,4,5]
let numberSet2 : Set<Int> = [6,7,8,9,10]
let numberSet3 : Set<Int> = [11,12,13,14,15]
let randomNo = [3,6,9,11]
numberSets = [numberSet1,numberSet2,numberSet3]
}
func searchFor(){
for num in randomNo{
for set in numberSets{
if set.contains(num) {
print("The following number was found: ", num)
}
}
}
}
One way to do this is to continue the outer loop:
outer: for num in randomNo{
for set in numberSets{
if set.contains(num) {
print("The following number was found: ", num)
continue outer
}
}
}
Another way is to union all three sets:
let union = numberSet1.union(numberSet2).union(numberSet3)
print(randomNo.filter(union.contains))
First, I think it worth to mention that, in your example the code is not cycling through the sets, rather than arrays of sets (randomNo, numberSets).
If I get the problem right, you do not need to optimize looking up for element in set. Asking whether set contains element or not (a lookup), is not an expensive operation and has complexity of O(1).
If want to stop iterating through the numberSets once first number is found, just use break control flow statement:
func searchFor() {
for num in randomNo {
for set in numberSets {
if set.contains(num) {
print("The following number was found: ", num)
break
}
}
}
}
Hope it helps.
I built this code sample in Swift Playgrounds as a proof-of-concept for part of a larger project that I'm working on. What I need to do is pass in a series of options (represented by optionsArray or testArray) where each int is the number of options available. These options will eventually be built into 300+ million separate PDFs and HTML files. The code currently works, and puts out the giant list of possibilities that I want it to.
My question is this: Is there a better approach to handling this kind of situation? Is there something more elegant or efficient? This is not something that will be run live on an app or anything, it will run from a command line and take all the time it needs, but if there is a better approach for performance or stability I'm all ears.
Things I already know: It can't handle a value of 0 coming out of the array. The array is a constant, so it won't happen by accident. The way the code down the line will handle things, 0 is a nonsensical value to use. Each element represents the number of options available, so 2 is essentially a Boolean, 1 would be false only. So if I needed placeholder elements for future expansion, they would be a value of 1 and show up as a 0 in the output.
Also, the final product will not just barf text to the console as output, it will write a file in the permutationEnding() function based on the currentOptions array.
let optionsArray: [Int] = [7,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,3,2,2,2,2,2,2,2,2]
let testArray: [Int] = [7,2,3,2]
var currentOptions: [Int] = []
var outputString: String = ""
func buildPermutations(array: Array<Int>) {
currentOptions.removeAll()
permutationRecursion(array: array, index: 0)
}
func permutationRecursion(array: Array<Int>, index: Int) {
for i in 1 ... array[index] {
currentOptions.append(Int(i-1))
if array.count > (index + 1) {
permutationRecursion(array: array, index: index + 1)
} else {
permutationEnding()
}
currentOptions.removeLast()
}
}
func permutationEnding() {
for i in 1 ... currentOptions.count { // Output Elements
outputString += String(currentOptions[i-1])
}
outputString += "\n" // Goes after output elements closing bracket.
}
// buildPermutations(array: optionsArray)
buildPermutations(array: testArray)
print(outputString)
Thoughts?
I think I've figured out what you're trying to do. You want a string output of every possible integer combination that could map all possible routes on the decision tree.
I got it down to four or five lines.
let n = testArray.count // for readability
let products = ([Int](1...n)).map({testArray[$0..<n].reduce(1, *)})
// products is the cross product of element i + 1 to element n of the array for all i in the array
let zipped = zip(testArray, products)
for i in 0..<testArray.reduce(1, *) { // this reduce is the cross product of the whole array
let treePath = zipped.map(){ String(i / $0.1 % $0.0) }.joined()
outputString += treePath + "\n"
}
One more edit: I think this might be faster with some fancy matrix operations like NumPy. I wonder if the Accelerate framework could do some magic for you, but I have not worked with it.
edit: I was curious so I timed it with this test array
let testArray: [Int] = [7,2,2,2,2,2,2,3,2]
The recursive function in the question was: 132.56 s
The zip-map here was: 14.44 s
And it appears to be exponential as I add elements to the test array.
I'm new to programming and have been learning Swift by doing a number of online courses. In one of the courses we built a basic trivia game and I've been progressively trying to improve it by doing my own coding (best way to learn!).
Recently I came across what's called a Fisher-Yates shuffle and, after much trial and error (and with the help of the stack overflow community) was able to use GKRandomSource from Swift's Gameplaykit to shuffle my trivia questions around so that they were being asked randomly. This was an improvement on the original arc4random code I was using because the shuffle removed questions already asked from the overall pool of questions, thereby ensuring that they did not repeat (at least in iOS9).
This works well within the session, but once the user quits the app and relaunches it, the shuffle starts from scratch. So I was looking at a way to have the app 'remember' the questions already asked between sessions. My research led me to the idea of seeding and I've been trying to get this to work with my GKRandomSource code, but I'm obviously missing something.
Any advice etc would be most welcome - especially since I'm not entirely sure that this 'seeding' approach will achieve my ultimate aim of not repeating questions already asked in previous sessions of the app.
Below are what I believe to be the relevant bits of my revised code.
All questions and potential answer choices are stored in a .json file as such:
{
"id" : "1",
"question": "Earth is a:",
"answers": [
"Planet",
"Meteor",
"Star",
"Asteroid"
],
"difficulty": "1"
}
I use the following code to load the .json file:
func loadAllQuestionsAndAnswers()
{
let path = NSBundle.mainBundle().pathForResource("content", ofType: "json")
let jsonData : NSData = NSData(contentsOfFile: path!)!
allEntries = (try! NSJSONSerialization.JSONObjectWithData(jsonData, options: NSJSONReadingOptions.MutableContainers)) as! NSArray
//println(allEntries)
}
And below is my most recent code for trying to achieve the shuffle of all questions and replicate it in future sessions):
var allEntries : NSArray!
var shuffledQuestions: [AnyObject]!
var nextQuestion = -1
var mySeededQuestions : [AnyObject]
loadAllQuestionsAndAnswers()
if #available(iOS 9.0, *) {
let lcg = GKLinearCongruentialRandomSource(seed: mySeededQuestions)
let shuffledQuestions = lcg.arrayByShufflingObjectsInArray(allEntries)
nextQuestion++
loadQuestion(nextQuestion)
// Fallback on earlier versions
}else{
let randomNumber = Int(arc4random_uniform(UInt32(allEntries.count)))
loadQuestionPreiOS9(randomNumber)
}
I know at the very least I have a problem with the above code, but I'm at a loss. I'm also thinking that maybe I'm missing a step in terms of storing the seed?
For the sake of completeness, I use a label to display the question and four images to display the potential answers, using the following code:
func loadQuestion(index : Int)
{
let entry : NSDictionary = shuffledQuestions[index] as! NSDictionary
let question : NSString = entry.objectForKey("question") as! NSString
let arr : NSMutableArray = entry.objectForKey("answers") as! NSMutableArray
//println(question)
//println(arr)
labelQuestion.text = question as String
let indices : [Int] = [0,1,2,3]
//let newSequence = shuffle(indices)
let newSequence = indices.shuffle()
var i : Int = 0
for(i = 0; i < newSequence.count; i++)
{
let index = newSequence[i]
if(index == 0)
{
// we need to store the correct answer index
currentCorrectAnswerIndex = i
}
let answer = arr.objectAtIndex(index) as! NSString
switch(i)
{
case 0:
buttonA.setTitle(answer as String, forState: UIControlState.Normal)
break;
case 1:
buttonB.setTitle(answer as String, forState: UIControlState.Normal)
break;
case 2:
buttonC.setTitle(answer as String, forState: UIControlState.Normal)
break;
case 3:
buttonD.setTitle(answer as String, forState: UIControlState.Normal)
break;
default:
break;
}
}
buttonNext.hidden = true
// we will need to reset the buttons to reenable them
ResetAnswerButtons()
}
func loadQuestionPreiOS9(index : Int)
{
let entry : NSDictionary = allEntries.objectAtIndex(index) as! NSDictionary
let question : NSString = entry.objectForKey("question") as! NSString
let arr : NSMutableArray = entry.objectForKey("answers") as! NSMutableArray
//println(question)
//println(arr)
labelQuestion.text = question as String
let indices : [Int] = [0,1,2,3]
//let newSequence = shuffle(indices)
let newSequence = indices.shuffle()
var i : Int = 0
for(i = 0; i < newSequence.count; i++)
{
let index = newSequence[i]
if(index == 0)
{
// we need to store the correct answer index
currentCorrectAnswerIndex = i
}
let answer = arr.objectAtIndex(index) as! NSString
switch(i)
{
case 0:
buttonA.setTitle(answer as String, forState: UIControlState.Normal)
break;
case 1:
buttonB.setTitle(answer as String, forState: UIControlState.Normal)
break;
case 2:
buttonC.setTitle(answer as String, forState: UIControlState.Normal)
break;
case 3:
buttonD.setTitle(answer as String, forState: UIControlState.Normal)
break;
default:
break;
}
}
buttonNext.hidden = true
// we will need to reset the buttons to reenable them
ResetAnswerButtons()
}
Finally, I use the following code to present the user with a 'Next' button after they've answered a question:
#IBAction func PressedButtonNext(sender: UIButton) {
print("button Next pressed")
if #available(iOS 9.0, *) {
nextQuestion++
loadQuestion(nextQuestion)
}else{
let randomNumber = Int(arc4random_uniform(UInt32(allEntries.count)))
loadQuestionPreiOS9(randomNumber)
}
I know my coding is probably quite verbose and unnecessary, but up until this latest improvement it's been working fine and I actually understand most of it (I think!)
There are really two questions here: what you're asking about and what you seem to want. They're both worth answering for different reasons, so...
How to seed a GK(Whatever)RandomSource
(All the GKRandomSource subclasses have seeds, even though the superclass GKRandomSource itself doesn't... that's because each class has its own data type for seeds. But the usage is the same.)
The critical bits of the code you've posted don't even compile due to a type mismatch: the seed/init(seed:) value for GKLinearCongruentialRandomSource is an integer, not an array of objects. The documentation for that value spells out what it's for (emphasis added) and how to use it:
Any two random sources initialized with the same seed data will generate the same sequence of random numbers. To replicate the behavior of an existing GKLinearCongruentialRandomSource instance, read that instance’s seed property and then create a new instance by passing the resulting data to the initWithSeed: initializer.
So, if you want to replicate a sequence of random numbers:
Create a random source with the plain initializer.
let source = GKLinearCongruentialRandomSource()
Save off that source's seed value.
let seed = source.seed // -> some UInt64 value
// write seed to user defaults, a file, a web service, whatever.
Use that random source for whatever.
Later, when you launch again and want the same sequence, read in the seed value and create a random source using the seed.
let seed = // read in seed value from wherever you saved it
let source = GKLinearCongruentialRandomSource(seed: seed)
This still doesn't get you what you're actually looking for, though: If source in step 1 produced the sequence 1, 6, 3, 9, 2, 7, source from step 4 will also produce the sequence 1, 6, 3, 9, 2, 7 — the seed doesn't record where you "left off" in a sequence. Or, since you're using it for an array shuffle, it'll produce the same shuffled ordering of the array as the first shuffle, but it doesn't remember what you did with the shuffled array thereafter.
How to use a shuffled ordering across multiple app launches
If you want to shuffle an array, walk through it in order, and then on a later run of your app continue walking through the same shuffled array from where you left off, you need to design around that requirement.
Shuffle on the first launch.
Record something about the ordering produced. (Say, a mapping of indices in the shuffle to indices in the original data.)
When walking through the shuffled array, record how far you've gone through it.
On later runs of the app, use the record of the ordering and the record of progress to decide where you are.
Here's a rough pass at that. (Note that I'm not touching your data model — this is a program design question, and SO is not a coding service. You'll need to think about how to flesh out this design to match your model and its use cases.)
struct Defaults {
static let lastQuestionIndex = "lastQuestionIndex"
static let questionOrder = "questionOrder"
}
let questions: [Question] // array of model objects, always in fixed order
func nextQuestion() -> Question {
let defaults = NSUserDefaults.standardUserDefaults()
if let lastIndex = defaults.integerForKey(Defaults.lastQuestionIndex) {
// we've run before, load the ordering
guard let shuffledOrder = defaults.arrayForKey(Defaults.questionOrder) as? [Int]
else { fatalError("save questionOrder with lastQuestionIndex") }
// advance the saved index so the next call to this function
// will get the next question
if lastIndex + 1 < count {
defaults.setInteger(lastIndex + 1, forKey: Defaults.lastQuestionIndex)
} else {
// ran out of shuffled questions, forget the order so we
// can reshuffle on the next call
defaults.removeObjectForKey(Defaults.questionOrder)
defaults.removeObjectForKey(Defaults.lastQuestionIndex)
}
// map lastQuestionIndex from sequential to shuffled
// and return the corresponding answer
let shuffledIndex = shuffledOrder[lastIndex]
return questions[shuffledIndex]
} else {
// first run, shuffle the question ordering (not the actual questions)
let source = GKRandomSource()
let sequentialOrder = Array(0..<questions.count)
let shuffledOrder = source.arrayByShufflingObjectsInArray(sequentialOrder)
// save the ordering, and the fact that we're asking the first question
defaults.setObject(shuffledOrder, forKey: Defaults.questionOrder)
defaults.setInteger(0, forKey: Defaults.lastQuestionIndex)
// return the first question in the shuffled ordering
let shuffledIndex = shuffledOrder[0]
return questions[shuffledIndex]
}
}
That's probably a bit pseudocode-ish (so you might need to worry about casting arrays to work with NSUserDefaults, etc), but as a general design it should be enough to give you some food for thought.
You can also use the following to drop off a certain amount of values so if you keep a roll count dropping that many on next start is as easy as :
arc4.dropValues(rollCount)