I'm trying to show a tableview similar to contacts with my list of users.
I declare a global variable of friends that will store the first character of a name and a list of users whose first name start with that
var friends = [Character: [User]]()
In my fetch method, I do this
for friend in newFriends {
let letter = friend.firstName?[(friend.firstName?.startIndex)!]
print(letter)
self.friends[letter!]?.append(friend)
}
After this, I should have my friends array with the first letter of the name and the users that fall in it; however, my friends dictionary is empty.
How do I fix this?
Edit: I'm following this tutorial and he doesnt exactly the same.. Swift: How to make alphabetically section headers in table view with a mutable data source
Rather than using Character as the key, use String. You need to be sure to init the [User] array for every new First Initial key you insert into groupedNames. I keep an array of groupedLetters to make it easier to get a section count
var groupedNames = [String: [User]]()
var groupedLetters = Array<String>()
func filterNames() {
groupedNames.removeAll()
groupedLetters.removeAll()
for friend in newFriends {
let index = friend.firstName.index(friend.firstName.startIndex, offsetBy: 0)
let firstLetter = String(friend.firstName[index]).uppercased()
if groupedNames[firstLetter] != nil {
//array already exists, just append
groupedNames[firstLetter]?.append(friend)
} else {
//no array for that letter key - init array and store the letter in the groupedLetters array
groupedNames[firstLetter] = [friend]
groupedLetters.append(firstLetter)
}
}
}
Creating a Dictionary structure with Characters as keys & values as Array of User will be more succinct.
The error occurs because you are declaring an empty dictionary, that means you have to add a key / empty array pair if there is no entry for that character.
Consider also to consolidate the question / exclamation marks
class User {
let firstName : String
init(firstName : String) {
self.firstName = firstName
}
}
var friends = [Character: [User]]()
let newFriends = [User(firstName:"foo"), User(firstName:"bar"), User(firstName:"baz")]
for friend in newFriends {
let letter = friend.firstName[friend.firstName.startIndex]
if friends[letter] == nil {
friends[letter] = [User]()
}
friends[letter]!.append(friend)
}
Related
I have a dictionary that holds objects, inside that objects I have an id, is there a way to check matches with this id and return the object?
example:
if I have id = 2 and I want to check if there exists in the object and get the particular object that matches with this id
Thanks for the help
my structs:
struct CoinsInfo:Codable {
let data:[String:CoinSpecificInfo]?
}
struct CoinSpecificInfo:Codable {
let urls:UrlsCoins?
let logo:String?
let id:Int?
let symbol:String?
}
You can try
// item is an instance of CoinsInfo
// get a new dictionary with all keys that has id matching in their value
guard let matches = item.data?.filter { $1.id == 2 } else { return }
// get an array of objects
let arr = Array(matches.values)
So I have managed to retrieve some data from Firebase and it looks like this when printed:
[Resturant.CustomerList(key: "-LQQlhEmNZb8Kaha9uCk", customerLastName:
“Kendrick”, customerFirstName: “Anna”, customerSeat: "100",
customerOrder: “Noodle”, Timestamp: 1541290545703.0)]
Question: How do I unwrap them so I can put individual value into other String variables?
I tried many ways but I get errors such cannot subscript a value of type [CustomerList] with an index of type String if I do something like let custName = self.list["Name"] as? String
ps. CustomerList is a struct
pps. The print out of list is what is shown
As you have a list of CustomerList objects i.e, [CustomerList] so you should first get a single object from this list. Lets say we want the very first object from this list to access its properties then we can do it as below,
if let firstCustomer = self.list.first {
let firstName = firstCustomer.customerFirstName
let lastName = firstCustomer.customerLastName
}
If you want to access an object at a specific index then you can do as below,
let index = 0
let customer = self.list[index]
let firstName = customer.customerFirstName
let lastName = customer.customerLastName
To find a particular customer, you can filter that as below,
let johny = self.list.filter{ $0.customerFirstName == "Jonhny"}.first {
print(johny.customerLastName)
}
To get a custom list created from the customers list, you can use map as below,
let lastNamesArray = self.list.map({ $0.customerLastName })
class Employee{
var id:Int
var name:String
var salary:Int
init(){
self.id=0
self.name=""
self.salary=0
}
func getInfo(){
self.name=readLine()!
self.id=Int(readLine()!)!
self.salary=Int(readLine()!)!
}
}
var count=0
var flag="y"
var empData:[Employee]=[]
repeat{
count+=1
empData[count]=Employee()
empData[count].getInfo()
flag=readLine()!
}while(flag=="y") `
I have a class Employee with properties id , nam and salary. The function getInfo() is used to get information from user. I want to read data until the flag!="y" . I am getting index out of range error.
What is the right way of inputting data? Can we index the objects ?
You need to append to your array to make it increase in size. Replace
empData[count]=Employee()
with
empData.append(Employee())
to avoid index out of range error
Update
To make your code a little less horrible I would do
repeat {
var employee = Employee()
employee.getInfo()
empData.append(employee)
flag=readLine()!
}while( flag == "y" )
The subscript operator cannot be used to add elements to an array index which doesn't exist yet. You either need to initialize the array with an element count if you know at the time of initialization how many elements your array will have or use the append operator to add new elements to the array after the last index.
You don't even need the count variable, as you can simply access empData.last safely after calling append and adding a new Employee to the Array.
var flag="y"
var empData:[Employee]=[]
repeat {
empData.append(Employee())
empData.last!.getInfo()
flag=readLine()!
} while(flag=="y")
I would advise you to seriously reconsider your implementation as it is really unsafe at the moment. You are not validating user input in any way, hence your getInfo function can easily cause runtime errors if the user input is not in the expected form. Moreover, creating an empty initializer for Employee doesn't make sense, you could simply create a failable initializer, where you read the input and if the input is not of the correct form, make the initializer return nil.
class Employee{
let id:Int
let name:String
let salary:Int
init?(){
guard let name = readLine() else { return nil }
self.name = name
guard let idString = readLine(), let id = Int(idString) else { return nil }
self.id = id
guard let salaryString = readLine(), let salary = Int(salaryString) else { return nil}
self.salary = salary
}
}
var flag="y"
var empData:[Employee]=[]
repeat {
if let employee = Employee() {
empData.append(employee)
} else {
// Display error message to the user
}
flag=readLine() ?? ""
} while(flag=="y")
I'm new to this forum! I am having a little bit of trouble sorting my Person's array with the use of UILocalizedIndexedCollation.
Code
I created the following class:
#objc class Person : NSObject {
#objc var firstName: String!
#objc var lastName: String!
init(firstName: String, lastName: String) {
self.firstName = firstName
self.lastName = lastName
}
}
With the help of this class, I created a bunch of instances to be displayed and sorted alphabetically on the table view by their last names.
For me to do so, I created the following function:
func partitionObjects(array:[AnyObject], collationStringSelector:Selector) -> ([AnyObject], [String]) {
var unsortedSections = [[AnyObject]]()
//1. Create a array to hold the data for each section
for _ in self.sectionTitles {
unsortedSections.append([]) //appending an empty array
}
//2. Put each objects into a section
for item in array {
let index:Int = self.section(for: item, collationStringSelector:collationStringSelector)
unsortedSections[index].append(item)
}
//3. sorting the array of each sections
var sectionTitles = [String]()
var sections = [AnyObject]()
sectionTitles.append("Frequently Requested")
for index in 0 ..< unsortedSections.count { if unsortedSections[index].count > 0 {
sectionTitles.append(self.sectionTitles[index])
sections.append(self.sortedArray(from: unsortedSections[index], collationStringSelector: collationStringSelector) as AnyObject)
}
}
return (sections, sectionTitles)
}
With this function, I am able to assign my array of Person and array of titles to the returning values of the function:
var sectionTitles = [Person]()
var personsWithSections = [[Person]]()
var contacts = [Person]()
#objc func setUpCollation(){
let (arrayPersons, arrayTitles) = collation.partitionObjects(array: self.persons, collationStringSelector: #selector(getter: Person.lastName))
self.personsWithSections = arrayPersons as! [[Person]]
self.sectionTitles = arrayTitles
}
With this, I am able able to set up my whole table view and it works great. I get every person sorted up by their last name to their corresponding alphabetical section.
The Issue, Specifically
The problem is that if the user has only inputed their first name and not their last name, that Person object gets appended to the last section of the array, where objects with last names that start with numbers or special characters go.
How can I append these object's with only first names to the corresponding alphabetical
section if the user doesn't input a last name? The same goes with
numbers.
As you can see, my collationsStringSelector takes Person.lastName, I was thinking maybe I could create a computed variable that would return the right person's property under some conditions? I am not sure how I would do so. It would be nice to have some guidance or help!
ps: NEW to the forum! if I'm doing something wrong let me know guys! thanks
I'm saving lists in a dictionary. These lists need to be updated. But when searching for an item, I need [] operator. When I save the result to a variable, a copy is used. This can not be used, to change the list itself:
item = dicMyList[key]
if item != nil {
// add it to existing list
dicMyList[key]!.list.append(filename)
// item?.list.append(filename)
}
I know, that I need the uncommented code above, but this accesses and searches again in dictionary. How can I save the result, without searching again? (like the commented line)
I want to speed up the code.
In case you needn't verify whether the inner list was actually existing or not prior to adding element fileName, you could use a more compact solution making use of the nil coalescing operator.
// example setup
var dicMyList = [1: ["foo.sig", "bar.cc"]] // [Int: [String]] dict
var key = 1
var fileName = "baz.h"
// "append" (copy-in/copy-out) 'fileName' to inner array associated
// with 'key'; constructing a new key-value pair in case none exist
dicMyList[key] = (dicMyList[key] ?? []) + [fileName]
print(dicMyList) // [1: ["foo.sig", "bar.cc", "baz.h"]]
// same method used for non-existant key
key = 2
fileName = "bax.swift"
dicMyList[key] = (dicMyList[key] ?? []) + [fileName]
print(dicMyList) // [2: ["bax.swift"], 1: ["foo.sig", "bar.cc", "baz.h"]]
Dictionaries and arrays are value types. So if you change an entry you'll need to save it back into the dictionary.
if var list = dicMyList[key] {
list.append(filename)
dicMyList[key] = list
} else {
dicMyList[key] = [filename]
}
It's a little bit late, but you can do something like this:
extension Optional where Wrapped == Array<String> {
mutating func append(_ element: String) {
if self == nil {
self = [element]
}
else {
self!.append(element)
}
}
}
var dictionary = [String: [String]]()
dictionary["Hola"].append("Chau")
You can try this in the Playground and then adapt to your needs.