I'm learning Swift as I go here, so apologies if this is a silly question.
I'm looking to use the output of one function (String) to determine an input into a different function (Array).
The first function output (String) is then combined with another String to form the name of an already defined Array, which i'd like to use as input to second function. However, despite having the same name, the String is not seen as an array.
I've skipped some of the code, but relevant section below.
// Defined array
let rushProb = [0,11,19,64,78,89,96,98,99,100]
// Define probability and outcome function - PlayType
func findPlay(prob: [Int], outcome: [String]) -> String {
if let index = prob.firstIndex(where: { $0 > Int.random(in: 1...100) }) {
return outcome[index]
}
else {
return "na"
}
}
// This is successfully output as "rush"
let playSel = findPlay(prob: scen1Prob, outcome: scenPlay)
// This then creates "rushProb"
let playSelProb = playSel+"Prob"
// I want this to ultimately be findYards(prob: rushProb)
findYards(prob: playSelProb)
Well, you could use a dictionary where the key replaces your array name, and the value is the array. Then, you'd use the name you create to look up the array value in the dictionary:
let arrays = ["rushProb": [0,11,19,64,78,89,96,98,99,100],
"fooProb" : [0,15,29,44,68,78,86,92,94,100]]
// This is successfully output as "rush"
let playSel = findPlay(prob: scen1Prob, outcome: scenPlay)
// This then creates "rushProb"
let playSelProb = playSel+"Prob"
// look up the array that corresponds to "rushProb"
if let array = arrays[playSelProb] {
findYards(prob: array)
}
Related
Say I have the following array:
var questions = ["Is he great?", "Is he nice?", "Is he wonderful?"]
How can I alter it so that if I call any element from this array, the 'he' is substituted for 'she'? I've tried map, but this only seems to work for individual elements, and not parts of an element. Slicing is also only inter-element, and replaceOccurrence creates a new string, but doesn't alter the original. Ideally I'd like to write:
print(questions[0])
and get: "Is she great?" for any element in the array containing 'he' without having to create a whole new array. TIA.
I am not sure why you want to avoid creating a new array, but if you're determined to avoid making new arrays, consider an array of functions that return the thing you want, like:
var sheOrHe = "he"
func f(_ s: String) -> () -> String {
return { "Is \(sheOrHe) \(s)?" }
}
let qFuncs = [f("great"), f("nice"), f("wonderful")]
qFuncs[0]() // "Is he great?"
sheOrHe = "she"
qFuncs[0]() // "Is she great?"
Or without closing over the sheOrHe var:
func f(_ s: String) -> (String) -> String {
{ sheOrHe in "Is \(sheOrHe) \(s)?" }
}
let qFuncs = [f("great"), f("nice"), f("wonderful")]
qFuncs[0]("he") // "Is he great?"
qFuncs[0]("she") // "Is she great?"
Or without storing the functions:
func areThey(_ s: String) -> (String) -> String {
{ sheOrHe in "Is \(sheOrHe) \(s)?" }
}
let adjectives = ["great", "nice", "wonderful"]
areThey(adjectives[0])("he") // "Is he great?"
areThey(adjectives[0])("she") // "Is she great?"
I have a fixed size array of Strings: [String; 2]. I want to turn it into a (String, String). Can I do this without copying the values?
The piece of code that I'm working on in particular is the following:
let (basis, names_0, names_1) = if let Some(names) = self.arg_name {
(ComparisonBasis::Name, names[0], names[1])
} else {
(ComparisonBasis::File, self.arg_file[0], self.arg_file[1])
};
types:
self.arg_name: Option<[String; 2]>
self.arg_file: Vec<String>
Right now I'm getting errors
cannot move out of type `[std::string::String; 2]`, a non-copy fixed-size array [E0508]
and
cannot move out of indexed content [E0507]
for the two arms of the if
You've omitted a fair amount of context, so I'm taking a guess at a few aspects. I'm also hewing a little closer to the question you asked, rather than the vaguer one implied by your snippets.
struct NeverSpecified {
arg_names: Option<[String; 2]>,
arg_file: Vec<String>,
}
impl NeverSpecified {
fn some_method_i_guess(mut self) -> (String, String) {
if let Some(mut names) = self.arg_names {
use std::mem::replace;
let name_0 = replace(&mut names[0], String::new());
let name_1 = replace(&mut names[1], String::new());
(name_0, name_1)
} else {
let mut names = self.arg_file.drain(0..2);
let name_0 = names.next().expect("expected 2 names, got 0");
let name_1 = names.next().expect("expected 2 names, got 1");
(name_0, name_1)
}
}
}
I use std::mem::replace to switch the contents of the array, whilst leaving it in a valid state. This is necessary because Rust won't allow you to have a "partially valid" array. There are no copies or allocations involved in this path.
In the other path, we have to pull elements out of the vector by hand. Again, you can't just move values out of a container via indexing (this is actually a limitation of indexing overall). Instead, I use Vec::drain to essentially chop the first two elements out of the vector, then extract them from the resulting iterator. To be clear: this path doesn't involve any copies or allocations, either.
As an aside, those expect methods shouldn't ever be triggered (since drain does bounds checking), but better paranoid than sorry; if you want to replace them with unwrap() calls instead, that should be fine..
Since Rust 1.36, you can use slice patterns to bind to all the values of the array at once:
struct NeverSpecified {
arg_names: Option<[String; 2]>,
arg_file: Vec<String>,
}
impl NeverSpecified {
fn some_method_i_guess(mut self) -> (String, String) {
if let Some([name_0, name_1]) = self.arg_names.take() {
(name_0, name_1)
} else {
let mut names = self.arg_file.drain(0..2);
let name_0 = names.next().expect("expected 2 names, got 0");
let name_1 = names.next().expect("expected 2 names, got 1");
(name_0, name_1)
}
}
}
See also:
Method for safely moving all elements out of a generic array into a tuple with minimal overhead
I am currently learning swift and am experimenting with data structures. In may code I have certain routines with a name(String) and several tasks(Array of Strings). These values are in a structure.
So I am trying to add another value to the array after it has been initialized. My code is actually working, however I really think it very weird and odd and DO NOT think, that it is the way it should be done.
var routineMgr: routineManager = routineManager();
struct routine{
var name = "Name";
var tasks = [String]();
}
class routineManager: NSObject {
var routines = [routine]();
func addTask(name: String, desc: String){
//init routines with name and an array with certain values, here "Hallo" & "Moin"
routines.append(routine(name: name, tasks: ["Hallo","Moin"]));
//so i just put this part here to make the example shorter, but it would be in ad different function to make more sense
//adding a new value ("Salut") to the tasks array in the first routine
//getting current array
var tempArray = routines[0].tasks;
//appending new value to current value
tempArray.append("Salut");
//replacing old routine with a copy (same name), but the new array (with the appended salut)
routines[0] = routine(name: routines[0].name, tasks: tempArray);
}
}
I have tried some (to me) "more correct" ways, like:
routines[0].tasks.append("Salut");
But I always got tons of errors, which I also did not understand.
So my question now: How is it actually done correctly? And why does the second way not work?
Your help and advice is really appreciated!
You can create a function to append the values in the struct (that is what I would do). You can even use it to validade values or anything else you need to do before append, it can also return a boolean to let your code know if the value was successfully appended or not
var routineMgr: routineManager = routineManager();
struct routine{
var name = "Name";
var tasks = [String]();
mutating func addTask(task: String){
tasks.append(task)
}
}
class routineManager: NSObject {
var routines = [routine]();
func addTask(name: String, desc: String){
routines.append(routine(name: name, tasks: ["Hallo","Moin"]));
routines[0].addTask("Salut")
}
}
I hope that helps
I am learning how to build apps and working with Swift for this project.
I had a buddy help me pull data in from a website and it looks like he created classes with variables and mapped them to certain extensions (IE "Username") so when I call the variable data such as profile I would call it. The below uses luck_30 able to store "Stats.luck_30"
luck_30.text = profile.luck_30
So inside one of my variables that is in this "Profile" class is setup into an array. I can pull the array out of the class, but I can't seem to do for while statement replacing the [#] with a variable from the for command.
func aliveWorkers(profile: Profile) -> NSNumber{
var myworkers : Array = profile.workers!
//this test works and returns the proper value
var testworker: NSNumber = myworkers[0].alive!
println("The satus of the test worker is " + testworker.description)
/* This code is giving error "Could not find member alive" it does not ifor var
for ifor in myworkers{
var thisworker: NSNumber = myworkers[ifor].alive! as NSNumber
}
*/
return 42
}
Your variable ifor is not a counter, it is an actual object. You could do something like this:
for worker in myWorkers {
let workerIsAlive = worker.alive!
}
Alternatively, if you need the index,
for i in 0 ..< myWorkers.count {
let worker = myWorkers[i]
let workerIsAlive = worker.alive!
}
If you need both:
for (i, worker) in enumerate(myWorkers) {
let workerIsAlive = worker.alive!
}
And as a matter of style, I would stay away from NSNumber and use Int or Bool or whatever the data actually is. Also, it looks like the alive variable should not be optional, as you're unwrapping it everywhere. To avoid "mysterious" crashes later, you may want to think about making it a non-optional type.
when using a for in loop, your loop variable isn't an index, its the objects you're looping through. so..
func aliveWorkers() {
var myworkers = [1, 2, 3]
//this test works and returns the proper value
let testworker = myworkers[0]
print("The satus of the test worker is \(testworker)")
for ifor in myworkers {
print(ifor)
}
}
Notice a few things... you don't need to use + to concatenate those strings. you can just use string interpolation. \(variable) inserts the value of variable in the string.
Try to use let instead of var when you don't change the variable. You don't need to explicitly define type on variables either.
i use the following function to retrieve a random person from an array:
func getRandomPerson() -> String{
if(personArray.isEmpty){
return ""
} else {
var tempArray: [String] = []
for person in personArray{
tempArray += [person.getName()]
}
var unsignedArrayCount = UInt32(tempArray.count)
var unsignedRandomNumber = arc4random_uniform(unsignedArrayCount)
var randomNumber = Int(unsignedRandomNumber)
if tempArray.isEmpty {
return ""
} else {
return tempArray[randomNumber]
}
}
}
I would like to use this function inside an array of strings, Like this:
var theDares: [String] = ["Dare1 \(getRandomPerson())", "Dare2", "Dare3", "Dare4", "Dare5"]
But when i use the functions, it only runs the function once. Can you make the function run everytime you use the "Dare1" in this instance.
Thanks in advance
I think you are asking if you can set up your array so every time you fetch the object at index 0, it re-builds the value there.
The short answer is no. Your code is creating an array of strings, and the item at index 0 is built ONCE using a function call.
However, it is possible to make a custom class implement the subscript operator. You could create a custom object that looks like an array and allows you to index into it using an Int index. In response to the index operator you could run custom code that built and returned a random string.
Since it sounds like you're a beginning programmer creating a custom class the implements the subscript operator might be beyond your current abilities however.
Try like this:
let personArray = ["John", "Steve", "Tim"]
var randomPerson: String {
return personArray.isEmpty ? "" : personArray[Int(arc4random_uniform(UInt32(personArray.count)))]
}
println(randomPerson) // "Steve"