Just started learning swift, spent a few hours trying to figure this out by searching here but no luck so far.
I have an array, created like this:
class ProbabilitiesClass {
var list = [Odds]()
init() {
list.append(Odds(dateInit: -35, oddsTodayInit: "0,01", sevenDaysInit: "0,2"))
list.append(Odds(dateInit: -34, oddsTodayInit: "0,01", sevenDaysInit: "0,3"))
list.append(Odds(dateInit: -33, oddsTodayInit: "0,02", sevenDaysInit: "0,4"))
I want to search first parameter of this array for an integer and return its index.
Tried this
if let i = Odds.firstIndex(where: { $0.hasPrefix(differenceInDays) }) {
print("index is \([i])")
}
It returns error:
Type 'Odds' has no member 'firstIndex'
The end goal is to return second and third parameters of that index.
Update: I defined Odds like this:
import Foundation
class Odds {
let dateText : Int
let oddsToday : String
let odds7Days : String
init(dateInit: Int, oddsTodayInit: String, sevenDaysInit : String) {
dateText = dateInit
oddsToday = oddsTodayInit
odds7Days = sevenDaysInit
}
}
You could do it like so:
let p = ProbabilitiesClass()
let differenceInDays = -34
if let i = p.list.firstIndex(where: { $0.dateText == differenceInDays }) {
print("index is \([i])") //index is [1]
}
Look for the index in the list property of an instance of ProbabilitiesClass. And like the error message says: The class Odds is not an array to use the method firstIndex(where:) on it.
If you want to use the properties of the first element which has its dateInit equal to differenceInDays, then you could do it like so:
if let first = p.list.first(where: { $0.dateText == differenceInDays }) {
print("oddsTodayInit =", first.oddsToday)
print("sevenDaysInit =", first.odds7Days)
}
It uses this function first(where:).
Related
I am calling a function in order to do a select statement in a bundled SQLite database. The function returns an array of structs. The database is being read correctly as I have put some print commands in the code. However the final array only has 1 row in it, which contains all the data, instead of 16 rows of structs.
The struct code, which is in databaseHelper.swift, is...
struct ButtonData: Hashable {
let english: String
let categoryID: Int
let indonesian: String
}
The database code, in databaseHelper, is
class DatabaseHelper {
var buttonVars = [ButtonData]()
var database: Connection!
let buttonsTable = Table("Button")
let english = Expression<String>("english")
let category = Expression<String>("category")
let categoryID = Expression<Int>("ID")
let filename = Expression<String>("filename")
let indonesian = Expression<String>("indonesian")
init() {
do {
let path = Bundle.main.path(forResource: "sga", ofType: "db")!
let database = try Connection(path, readonly: true)
self.database = database
print("Database initialized at path \(path)")
} catch {
print("error")
}
}
func queryDatabase(passedCategory: String) -> [ButtonData] {
do {
let buttons = try self.database.prepare(self.buttonsTable.filter(self.category==passedCategory))
for row in buttons {
print("English: \(row[self.english]), ID: \(row[self.categoryID]), Indonesian: \(row[self.indonesian])")
// buttonVars.append(ButtonData(english: row[english], categoryID: row[categoryID], indonesian: row[indonesian]))
buttonVars.append(ButtonData(english: row[english], categoryID: row[categoryID], indonesian: row[indonesian]))
}
} catch {
print(error)
}
print(buttonVars[0])
print(buttonVars[1])
print(buttonVars[2])
print(buttonVars[3])
print(buttonVars[4])
print(buttonVars[5])
print(buttonVars[6])
print(buttonVars[7])
print(buttonVars[8])
print(buttonVars[9])
print(buttonVars[10])
print(buttonVars[11])
print(buttonVars[12])
print(buttonVars[13])
print(buttonVars[14])
print(buttonVars[15])
return buttonVars
}
}
The function code, which is in SoundPageView.swift (this page calls the database function), is...
func getArrayValues() {
let buttonRows = [DatabaseHelper().queryDatabase(passedCategory: category)]
let btnCount: Int = buttonRows.count
print(btnCount)
print(buttonRows[0])
}
The print values in the console show me that btnCount = 1 but before the array is returned, it is made of 16 rows. It is only after it is returned that it is reduced to 1 row.
Can anyone tell me what I'm doing wrong? I don't know how to access the data. Thanks.
I'm not sure why you are putting the brackets in this call:
let buttonRows = [DatabaseHelper().queryDatabase(passedCategory: category)]
The func queryDatabase returns an array on its own. I think it should be this:
let buttonRows = DatabaseHelper().queryDatabase(passedCategory: category)
Otherwise your result will be an array with one entry, which is the result of the call to queryDatabase.
I wrote a model like this as an exercise :
struct Store {
var name : String
var bills : Array<Bill>
var category : Category?
}
struct Bill {
var date : String
var amount : Float
}
struct Category {
var name : String
var tags : Array<String>
}
and when I'm searching if a store already exist to add a bill to it instead of creating a new store, my code doesn't work. It acts like if the result of the search is a copy of the Array element . I would like to have a reference.
var stores : Array <Store> = Array()
for billStatment in billStatements! {
let billParts = billStatment.split(separator: ",")
if billParts.count > 0 {
let bill : Bill = Bill(date:String(billParts[0]), amount: Float(billParts[2])!)
var store : Store = Store(name:String(billParts[1]), bills: [bill], category: nil)
if var alreadyAddedStore = stores.first(where: {$0.name == String(billParts[1])}) {
alreadyAddedStore.bills.append(bill)
print("yeah found it \(alreadyAddedStore)") // the debugger breaks here so I know the "first" method is working. If I print alreadyAddedStore here I have one more element, that's fine.
} else {
stores.append(store)
}
}
}
print("\(stores.count)") // If I break here for a given store that should contains multiple elements, I will see only the first one added in the else statement.
Can anyone tell me what I am doing wrong?
As already noted, you're confusing value (struct) semantics with reference (class) semantics.
One simple fix would be the change stores to a dictionary with the name as your key:
var stores : Dictionary<String, Store> = [:]
and use it like this:
if(stores[store.name] == nil) {
stores[store.name] = store
}
else {
stores[storeName].bills.append(bill)
}
I want to return the first item in a given array of custom objects and return an array of indices and the first custom object element so I can wrap a guard statement around it.
ie:
let firstOrder = existingOrders.enumerated().flatMap{$0,$1}.first
or attempt #1
let array = existingOrders.enumerated().map { (a, b) in return [$0.index : $1.element] }.first
or attempt #2
let array = existingOrders.enumerated().map { ($0.offset, $0.element) }.first
print (array)
This isn't returning the actual object; and it seems to return a tuple.
where
existingOrders = [ExistingOrder, EngineYard.ExistingOrder, EngineYard.ExistingOrder]
it returns the following;
[(0, EngineYard.ExistingOrder), (1, EngineYard.ExistingOrder), (2, EngineYard.ExistingOrder)]
attempt #3;
let array = existingOrders.enumerated().map { ($0.offset, $0.element) }
print (array)
guard let firstOrder = array.first else {
break
}
print (firstOrder) // should be a tuple of index and custom object
How do I grab the optional first item in an array and return index and element?
Many thanks
Edit. the reason I'm doing this is so that I can transfer the correct object to another class.
// transfer all
while (factory.existingOrders.count > 0) {
let array = myOrderBook.existingOrders.enumerated().map { ($0.offset, $0.element) }
guard let firstOrder = array.first else {
break
}
let index = (firstOrder.0)
factory.orderBook.transfer(index: index, destination: .completedOrder)
}
Where the Orderbook is a class;
Factory {
var orderBook:OrderBook = OrderBook()
}
OrderBook {
var existingOrders: [ExistingOrder] = [ExistingOrder]()
var completedOrders: [CompletedOrder] = [CompletedOrder]()
}
And the idea is that I want to transfer an object from existing orders to completed orders and vice versa
The function requires an index, but I guess I could refactor it so I can transfer an object instead.
The answer I was looking for was;
let array = myOrderBook.existingOrders.enumerated().map { ($0.offset, $0.element) }
However, I found that my code needed to be refactored.
Thanks.
Issue closed.
I created an array of objects:
var fullMonthlyList = [SimulationMonthly]()
The class here:
class SimulationMonthly {
var monthlyMonthDuration: NSNumber = 0
var monthlyYearDuration: NSNumber = 0
var monthlyFullAmount: NSNumber = 0
var monthlyAmount: Int = 0
init(monthlyMonthDuration: NSNumber, monthlyYearDuration: NSNumber, monthlyFullAmount: NSNumber, monthlyAmount: Int){
self.monthlyMonthDuration = monthlyMonthDuration
self.monthlyYearDuration = monthlyYearDuration
self.monthlyFullAmount = monthlyFullAmount
self.monthlyAmount = monthlyAmount
}
}
I just did append to populate it, now I want to find for example if they're an existing value, for example monthlyAmount equals to "194" by search in the array, how can I do ? I have tried filter and contains but I get errors.
What I've tried:
if self.fullMonthlyList.filter({ $0.monthlyAmount == self.monthlyAmount.intValue }) { ... }
Error:
Cannot invoke 'filter' with an argument list of type '((SimulationMonthly) throws -> Bool)'
You can do:
if let sim = fullMonthlyList.first(where: { $0.monthlyAmount == 194 }) {
// Do something with sim or print that the object exists...
}
This will give you the first element in your array where monthlyAmount equals 194.
If you want all elements with that condition, you can use filter:
let result = fullMonthlyList.filter { $0.monthlyAmount == 194 }
If you don't need the object at all but you just want to know if one exists, then contains would be enough:
let result = fullMonthlyList.contains(where: { $0.monthlyAmount == 194 })
Here's a simple playground example of filtering objects based on matching a property. You should be able to expand it to your situation.
class Item {
var value: Int
init(_ val: Int) {
value = val
}
}
var items = [Item]()
for setting in 0..<5 {
items.append(Item(setting))
}
func select(_ with: Int) -> [Item] {
return items.filter { $0.value == with }
}
let found = select(3)
I want to store structs inside an array, access and change the values of the struct in a for loop.
struct testing {
var value:Int
}
var test1 = testing(value: 6 )
test1.value = 2
// this works with no issue
var test2 = testing(value: 12 )
var testings = [ test1, test2 ]
for test in testings{
test.value = 3
// here I get the error:"Can not assign to 'value' in 'test'"
}
If I change the struct to class it works. Can anyone tell me how I can change the value of the struct.
Besides what said by #MikeS, remember that structs are value types. So in the for loop:
for test in testings {
a copy of an array element is assigned to the test variable. Any change you make on it is restricted to the test variable, without doing any actual change to the array elements. It works for classes because they are reference types, hence the reference and not the value is copied to the test variable.
The proper way to do that is by using a for by index:
for index in 0..<testings.count {
testings[index].value = 15
}
in this case you are accessing (and modifying) the actual struct element and not a copy of it.
Well I am going to update my answer for swift 3 compatibility.
When you are programming many you need to change some values of objects that are inside a collection. In this example we have an array of struct and given a condition we need to change the value of a specific object. This is a very common thing in any development day.
Instead of using an index to determine which object has to be modified I prefer to use an if condition, which IMHO is more common.
import Foundation
struct MyStruct: CustomDebugStringConvertible {
var myValue:Int
var debugDescription: String {
return "struct is \(myValue)"
}
}
let struct1 = MyStruct(myValue: 1)
let struct2 = MyStruct(myValue: 2)
let structArray = [struct1, struct2]
let newStructArray = structArray.map({ (myStruct) -> MyStruct in
// You can check anything like:
if myStruct.myValue == 1 {
var modified = myStruct
modified.myValue = 400
return modified
} else {
return myStruct
}
})
debugPrint(newStructArray)
Notice all the lets, this way of development is safer.
The classes are reference types, it's not needed to make a copy in order to change a value, like it happens with structs. Using the same example with classes:
class MyClass: CustomDebugStringConvertible {
var myValue:Int
init(myValue: Int){
self.myValue = myValue
}
var debugDescription: String {
return "class is \(myValue)"
}
}
let class1 = MyClass(myValue: 1)
let class2 = MyClass(myValue: 2)
let classArray = [class1, class2]
let newClassArray = classArray.map({ (myClass) -> MyClass in
// You can check anything like:
if myClass.myValue == 1 {
myClass.myValue = 400
}
return myClass
})
debugPrint(newClassArray)
To simplify working with value types in arrays you could use following extension (Swift 3):
extension Array {
mutating func modifyForEach(_ body: (_ index: Index, _ element: inout Element) -> ()) {
for index in indices {
modifyElement(atIndex: index) { body(index, &$0) }
}
}
mutating func modifyElement(atIndex index: Index, _ modifyElement: (_ element: inout Element) -> ()) {
var element = self[index]
modifyElement(&element)
self[index] = element
}
}
Example usage:
testings.modifyElement(atIndex: 0) { $0.value = 99 }
testings.modifyForEach { $1.value *= 2 }
testings.modifyForEach { $1.value = $0 }
How to change Array of Structs
for every element:
itemsArray.indices.forEach { itemsArray[$0].someValue = newValue }
for specific element:
itemsArray.indices.filter { itemsArray[$0].propertyToCompare == true }
.forEach { itemsArray[$0].someValue = newValue }
You have enough of good answers. I'll just tackle the question from a more generic angle.
As another example to better understand value types and what it means they get copied:
struct Item {
var value:Int
}
func change (item: Item, with value: Int){
item.value = value // cannot assign to property: 'item' is a 'let' constant
}
That is because item is copied, when it comes in, it is immutable — as a convenience.
Had you made Item a class type then you were able to change its value.
var item2 = item1 // mutable COPY created
item2.value = 10
print(item2.value) // 10
print(item1.value) // 5
This is very tricky answer. I think, You should not do like this:
struct testing {
var value:Int
}
var test1 = testing(value: 6)
var test2 = testing(value: 12)
var ary = [UnsafeMutablePointer<testing>].convertFromArrayLiteral(&test1, &test2)
for p in ary {
p.memory.value = 3
}
if test1.value == test2.value {
println("value: \(test1.value)")
}
For Xcode 6.1, array initialization will be
var ary = [UnsafeMutablePointer<testing>](arrayLiteral: &test1, &test2)
It is possible to use the map function to get this effect - essentially creating a new array
itemsArray = itemsArray.map {
var card = $0
card.isDefault = aCard.token == token
return card
}
I ended up recreating a new array of struct see the example below.
func updateDefaultCreditCard(token: String) {
var updatedArray: [CreditCard] = []
for aCard in self.creditcards {
var card = aCard
card.isDefault = aCard.token == token
updatedArray.append(card)
}
self.creditcards = updatedArray
}
I tried Antonio's answer which seemed quite logical but to my surprise it does not work. Exploring this further I tried the following:
struct testing {
var value:Int
}
var test1 = testing(value: 6 )
var test2 = testing(value: 12 )
var testings = [ test1, test2 ]
var test1b = testings[0]
test1b.value = 13
// I would assume this is same as test1, but it is not test1.value is still 6
// even trying
testings[0].value = 23
// still the value of test1 did not change.
// so I think the only way is to change the whole of test1
test1 = test1b