i am having the following for loop,
for (key, value) in changedDataDictionary {
// here i want to identify last key and value
}
I want to identify the execution of last object/ completion of the for loop
It may be very silly question, but i dont have any idea about that.
Thanks in advance.
This will work in general
var index: Int = 0
for (key, value) in changedDataDictionary {
index += 1;
if (index == changedDataDictionary.count) {
// do something
}
}
Note that a dictionary doesn't have a defined order so the last element will always be a different one and usually there is a better solution than using a tracking index.
If you just want to identify last key and element, you can also:
var lastKey: KeyType? = nil
var lastElement ValueType? = nil
for (key, value) in changedDataDictionary {
lastKey = key;
lastValue = value;
}
// do something with last key and value
Related
I'm trying to figure out how I can edit a value in a dictionary by testing for equality in a dictionaries keys against an array's value
So I've figured it out almost and I'm stuck trying to replace the value in the dictionary with a value that gets returned from a function.
for (key, value) in employeeSal {
for name in promotionList {
if key == name {
promotion(salary: value)
print(key, promotion(salary: value))
employeeSal[key: value]
}
}
}
The, print(key, promotion(salary: value), shows me exactly what I want it to. I tried to assign the new value to the key with, employeeSal[key: value], but it is not working and I'm out of ideas.
Assign the result of promotion to a variable. The. Use that to update the dictionary.
let newSalary = promotion(salary: value)
employeeSal[key] = newSalary
There’s a much more efficient solution:
for name in promotionList {
if let value = employeeSal[name] {
let newSalary = promotion(salary: value)
employeeSal[name] = newSalary
}
}
I am downloading information from a Firebase database and it is being inputted via a for loop into:
static var Reports = [String:[String:String]]()
I need to figure out a way to search the inside values for a certain string
I have messed around with this but can't seem to get it inside the inside dictionary (If that makes sense)
for values in Reports.count {
if let item = Reports["favorite drink"] {
print(item)
}
}
I need to have a search string then a number of times the value appears like so:
func findString(dict Dictionary) -> Int {
var ReportsLevel1 = 0
(for loop I'm guessing)
search here for string
return ReportsLevel1
}
Tip: the outside dictionary keys are not set in stone, they depend on what time and date the report was submitted
To find out the numberOfTimes in which "yourSearchString" appears you can do as follows
var numberOfTimes = 0
for internalDictionary in reports.values
{
for value in internalDictionary.values
{
if (value == "yourSearchString") { numberOfTimes += 1 }
}
}
or
let numberOfTimes = reports.flatMap { internalDictsArray in internalDictsArray.value.filter { $0.value == "yourSearchString" } }.count
I was wondering if there's a way to step through a dictionary in Swift. I know I can iterate through, but I was hoping to step one by one through a dictionary of items as the user taps a "next" button.
I was thinking I could initially iterate through the dictionary and store the keys in an array, then step through the keys and retrieve each item as needed, since the array can be indexed. This seems a little inelegant, though. Any thoughts?
My current approach:
var iterator = 0
var keys = [String]()
func loadKeys() {
for (key, value) in items {
keys.append(key)
}
}
func step() {
iterator += 1
let currentKey = keys[iterator]
let currentItem = items[currentKey]
}
I figure it would work just fine, just not sure it's the best practice.
Thanks for your help!
A dictionary also provides you with an iterator, so you can step through it using that:
var iterator = items.makeIterator()
func step() {
if let v = iterator.next() {
let currentKey = v.key
let currentValue = v.value
}
}
A dictionary is an indexed collection, so you can use a dictionary's index to step through the keys and values:
var i = items.startIndex
func step() {
guard i != items.endIndex else {
// at the end of the dictionary
return
}
let (currentKey, currentValue) = items[i]
i = items.index(after: i)
}
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.
I am currently using the following (clumsy) pieces of code for determining if a (non-empty) Swift dictionary contains a given key and for obtaining one (any) value from the same dictionary.
How can one put this more elegantly in Swift?
// excerpt from method that determines if dict contains key
if let _ = dict[key] {
return true
}
else {
return false
}
// excerpt from method that obtains first value from dict
for (_, value) in dict {
return value
}
You don't need any special code to do this, because it is what a dictionary already does. When you fetch dict[key] you know whether the dictionary contains the key, because the Optional that you get back is not nil (and it contains the value).
So, if you just want to answer the question whether the dictionary contains the key, ask:
let keyExists = dict[key] != nil
If you want the value and you know the dictionary contains the key, say:
let val = dict[key]!
But if, as usually happens, you don't know it contains the key - you want to fetch it and use it, but only if it exists - then use something like if let:
if let val = dict[key] {
// now val is not nil and the Optional has been unwrapped, so use it
}
Why not simply check for dict.keys.contains(key)?
Checking for dict[key] != nil will not work in cases where the value is nil.
As with a dictionary [String: String?] for example.
The accepted answer let keyExists = dict[key] != nil will not work if the Dictionary contains the key but has a value of nil.
If you want to be sure the Dictionary does not contain the key at all use this (tested in Swift 4).
if dict.keys.contains(key) {
// contains key
} else {
// does not contain key
}
Looks like you got what you need from #matt, but if you want a quick way to get a value for a key, or just the first value if that key doesn’t exist:
extension Dictionary {
func keyedOrFirstValue(key: Key) -> Value? {
// if key not found, replace the nil with
// the first element of the values collection
return self[key] ?? first(self.values)
// note, this is still an optional (because the
// dictionary could be empty)
}
}
let d = ["one":"red", "two":"blue"]
d.keyedOrFirstValue("one") // {Some "red"}
d.keyedOrFirstValue("two") // {Some "blue"}
d.keyedOrFirstValue("three") // {Some "red”}
Note, no guarantees what you'll actually get as the first value, it just happens in this case to return “red”.
My solution for a cache implementation that stores optional NSAttributedString:
public static var attributedMessageTextCache = [String: NSAttributedString?]()
if attributedMessageTextCache.index(forKey: "key") != nil
{
if let attributedMessageText = TextChatCache.attributedMessageTextCache["key"]
{
return attributedMessageText
}
return nil
}
TextChatCache.attributedMessageTextCache["key"] = .some(.none)
return nil
If you want to return the value of the key you can use this extension
extension Dictionary {
func containsKey(_ key: Key) -> Value? {
if let index = index(forKey: key){
return self.values[index]
}
return nil
}
}
if dictionayTemp["quantity"] != nil
{
//write your code
}
If you are dealing with dictionary that may contain nil value for a key then you can check existence of key by:
dictionay.index(forKey: item.key) != nil
For getting first value in dictionary:
dictionay.first?.value // optional since dictionary might be empty