Does anyone know here how to count amount of elements in all nested array of custom objects in Swift?
I.e. I have
[Comments] array which includes [Attachments] array. There may be 100 comments and 5 attachments in each of them. What is the most Swifty way to count all attachments in all comments? I tried few solutions like flatMap, map, compactMap, filter, reduce, but couldn't figure out how to achieve the desire result. The only one that worked for me was typical for in loop.
for comment in comments {
attachmentsCount += comment.attachments.count
}
Is there any better approach to achieve the same? Thanks
You can use reduce(_:_:) function of the Array to do that:
let attachementsCount = comments.reduce(0) { $0 + $1.attachments.count }
Here are two ways to do it based on using map
First with reduce
let count = comments.map(\.attachments.count).reduce(0, +)
And one variant using joined
let count = comments.map(\.attachments).joined().count
I have an array of drink toppings and want to remove the ones that aren't relevant to the drink, this is the code I have, but I can't figure out how to remove the topping from the array if it isn't within the criteria.
I can only remove at index path and this can change if we added more toppings etc so didn't seem accurate?
for toppings in self.toppings {
if self.selectedDrink.name == "Tea" {
if toppings.limit == "C" {
self.toppings.remove(at: toppings)
}
}
}
Essentially if the user selected Tea it looks for toppings limited for coffee and then I need to remove those ones that respond to the "C" property, but I can't see how?
Thanks for the help!
You can do in-place removal with a for loop, but it would be tricky, because you would need to iterate back to avoid disturbing indexes.
A simpler approach is to filter the array, and assign it back to the toppings property, like this:
toppings = toppings.filter {$0.limit != "C"}
I tried to display datas which is in Dictionary format. Below, three attempts are there. First attempt, output order is completely changed. Second attempt, output order is same as input. But, in third attempt, I declared variable as NSDictionary. Exact output I received. Why this changes in Dictionary? Kindly guide me. I searched for Swift's Dictionary tag. But I couldn't found out.
//First Attempt
var dict : Dictionary = ["name1" : "Loy", "name2" : "Roy"]
println(dict)
//output:
[name2: Roy, name1: Loy]
//Second Attempt
var dict : Dictionary = ["name2" : "Loy", "name1" : "Roy"]
println(dict)
//output:
[name2: Loy, name1: Roy]
-----------------------------------------------------------
//Third Attempt With NSDictionary
var dict : NSDictionary = ["name1" : "Loy", "name2" : "Roy"]
println(dict)
//output:
{
name1 = Loy;
name2 = Roy;
}
ANOTHER QUERY: I have used play ground to verify. My screen shot is below:
Here, In NSDictionary, I gave name5 as first, but in right side name2 is displaying, then, in println, it is displaying in ascending order. Why this is happening??
Here, In Dictionary, I gave name5 as first, but in right side name2 is displaying, then, in println, it is displaying, how it is taken on the Dictionary line. Why this is happening??
This is because of the definition of Dictionaries:
Dictionary
A dictionary stores associations between keys of the same type and values of the same type in an collection with no defined ordering.
There is no order, they might come out differently than they were put in. This is comparable to NSSet.
Edit:
NSDictionary
Dictionaries Collect Key-Value Pairs. Rather than simply maintaining an ordered or unordered collection of objects, an NSDictionary stores objects against given keys, which can then be used for retrieval.
There is also no order, however there is sorting on print for debugging purposes.
You can't sort a dictionary but you can sort its keys and loop through them as follow:
let myDictionary = ["name1" : "Loy", "name2" : "Roy", "name3" : "Tim", "name4" : "Steve"] // ["name1": "Loy", "name2": "Roy", "name3": "Tim", "name4": "Steve"]
let sorted = myDictionary.sorted {$0.key < $1.key} // or {$0.value < $1.value} to sort using the dictionary values
print(sorted) // "[(key: "name1", value: "Loy"), (key: "name2", value: "Roy"), (key: "name3", value: "Tim"), (key: "name4", value: "Steve")]\n"
for element in sorted {
print("Key = \(element.key) Value = \(element.value)" )
}
A little late for the party but if you want to maintain the order then use KeyValuePairs, the trade-off here is that if you use KeyValuePairs you lose the capability of maintaining unique elements in your list
var user: KeyValuePairs<String, String> {
return ["FirstName": "NSDumb",
"Address": "some address value here",
"Age":"30"]
}
prints
["FirstName": "NSDumb", "Address": "some address value", "Age": "30"]
Dictionaries, by nature, are not designed to be ordered, meaning that they're not supposed to be (although they can be!).
From the Dictionaries (Swift Standard Library documentation):
A dictionary is a type of hash table, providing fast access to the entries it contains. Each entry in the table is identified using its key, which is a hashable type such as a string or number. You use that key to retrieve the corresponding value, which can be any object. In other languages, similar data types are known as hashes or associated arrays.
This requires some basic knowledge of Data Structures, which I'll outline & oversimplify briefly.
Storing associated data without a dictionary
Consider for a minute if there was no Dictionary and you had to use an array of tuples instead, to store some information about different fruits and their colors, as another answer suggested:
let array = [
("Apple", "Red"),
("Banana", "Yellow"),
// ...
]
If you wanted to find the color of a fruit you'd have to loop through each element and check its value for the fruit, then return the color portion.
Dictionaries optimize their storage using hash functions to store their data using a unique hash that represents the key that is being stored. For swift this means turning our key—in this case a String—into an Int. Swift uses Int-based hashes, which we know because we all read the Hashable protocol documentation and we see that Hashable defines a hashValue property that returns an Int.
Storing associated data with a dictionary
The benefits of using a dictionary are that you get fast read access and fast write access to data; it makes "looking up" associated data easy and quick. Typically O(1) time complexity, although the apple docs don't specify, maybe because it depends on the key type's hash function implementation.
let dictionary = [
"Apple": "Red",
"Banana": "Yellow"
// ...
]
The trade off is that the order is typically not guaranteed to be preserved. Not guaranteed means that you might get lucky and it might be the same order, but it's not intended to be, so don't rely on it.
As an arbitrary example, maybe the string "Banana" gets hashed into the number 0, and "Apple" becomes 4. Since we now have an Int we could, under the hood, represent our dictionary as an array of size 5:
// what things *might* look like under, the hood, not our actual code
// comments represent the array index numbers
let privateArrayImplementationOfDictionary = [
"Yellow", // 0
nil, // 1
nil, // 2
nil, // 3
"Red", // 4
] // count = 5
You'll notice, we've converted our keys into array indices, and there are a bunch of blank spaces where we have nothing. Since we are using an array, we can insert data lightning fast, and retrieve it just as quickly.
Those nil spaces are reserved for more values that may come later, but this is also why when we try to get values out of a dictionary, they might be nil. So when we decide to add more values, something like:
dictionary["Lime"] = "Green" // pretend hashValue: 2
dictionary["Dragonfruit"] = "Pink" // pretend hashValue: 1
Our dictionary, under the hood, may look like this:
// what things *might* look like under, the hood, not our actual code
// comments represent the array index numbers
let privateArrayImplementationOfDictionary = [
"Yellow", // 0 ("Banana")
"Pink", // 1 ("Dragonfruit")
"Green", // 2 ("Lime")
nil, // 3 (unused space)
"Red", // 4 ("Apple")
] // count = 5
As you can see, the values are not stored at all in the order we entered them. In fact, the keys aren't even really there. This is because the hash function has change our keys into something else, a set of Int values that give us valid array indices for our actual storage mechanism, an array, which is hidden from the world.
I'm sure that was more information than you wanted and probably riddled with many inaccuracies, but it gives you the gist of how a dictionary works in practice and hopefully sounds better than, "that's just how it works."
When searching for the actual performance of Swift dictionaries, Is Swift dictionary ... indexed for performance? ... StackOverflow had some extra possible relevant details to offer.
If you're still interested to know more details about this, you can try implementing your own dictionary as an academic exercise. I'd also suggest picking up a book on Data Structures and Algorithms, there are many to choose from, unfortunately I don't have any suggestions for you.
The deeper you get into this topic the more you'll understand why you'll want to use one particular data structure over another.
Hope that helps!
✅ It is possible!
Although the Dictionary is not ordered, you can make it preserve the initial order by using the official OrderedDictionary from the original Swift Repo
The ordered collections currently contain:
Ordered Dictionary (That you are looking for)
Ordered Set
They said it is going to be merged in the Swift's source code soon (reference WWDC21)
Neither NSDictionary nor Swift::Dictionary orders its storage. The difference is that some NSDictionary objects sort their output when printing and Swift::Dictionary does not.
From the documentation of -[NSDictionary description]:
If each key in the dictionary is an NSString object, the entries are
listed in ascending order by key, otherwise the order in which the
entries are listed is undefined. This property is intended to produce
readable output for debugging purposes, not for serializing data.
From The Swift Programming Language:
A dictionary stores associations between keys of the same type and values of the same type in an collection with no defined ordering.
Basically, order of items as seen in output is arbitrary, dependant on internal implementation of data structure, and should not be relied on.
This is indeed an issue with dictionaries. However, there's a library available to make sure the order stays the way you initialised it.
OrderedDictionary is a lightweight implementation of an ordered dictionary data structure in Swift.
The OrderedDictionary structure is an immutable generic collection which combines the features of Dictionary and Array from the Swift standard library. Like Dictionary it stores key-value pairs and maps each key to a value. Like Array it stores those pairs sorted and accessible by a zero-based integer index.
Check it out here:
https://github.com/lukaskubanek/OrderedDictionary
Let's say I have an object with some number of properties and I load up 1000s of these objects into an array. Next, I perform a series of valueForKeyPaths against these properties:
result.property1 = [array valueForKeyPath:#"#sum.property1"];
result.property2 = [array valueForKeyPath:#"#sum.property2"];
result.property3 = [array valueForKeyPath:#"#sum.property3"];
etc...
Summing these properties individually seems pretty inefficient. Is there a better way besides fast enumerating over the properties and summing them manually? i.e.
for(Foo* foo in array) {
result.property1 += foo.property1;
result.property2 += foo.property2;
result.property3 += foo.property3;
}
KVC requires keys to be strings:
A key is a string that identifies a specific property of an object. Typically, a key corresponds to the name of an accessor method or instance variable in the receiving object. Keys must use ASCII encoding, begin with a lowercase letter, and may not contain whitespace.
So the answer as far as I know is unfortunately you can't do this with valueForKeyPath: you would have to manually do it or enumerate over it.
I have an XML file which is split up using pipes "|". I have some code in a question class that splits up the XML files "Items" as so..
List<string> questionComponents = newquestionString.Split('|').ToList<string>();
questionString = questionComponents[0];
apple = questionComponents[1];
pear = questionComponents[2];
orange = questionComponents[3];
correctAnswer = Int32.Parse(questionComponents[4]);
I want to compare these components with objects which are instantiated in my Game1 class (three fruit - apple, pear, orange). So how do I do this?
A friend helped me get this far. I have no idea how to do this, and after searching google with no luck I've resulted in asking here to you lovely people.
Thanks in advance :D
EDIT: To clear things up...
I have three objects called apple, pear and orange and I want to associate these objects with the strings which are shown in the XML file for each component of the strings. The question string displays a question, [1] answer 1, [2] answer 2, [3] answer [3].
And then I need a way to compare the answer to the object that is eaten in the game..
Assuming you have some kind of Orange object, some kind of Pear object, and some kind of Apple object, in each class override the ToString method.
If you have some generic Fruit or Answer object, consider passing a string in the constructor and returning that string in the ToString method.
EDIT: Since you've now clarified, I would go with Jonathan's idea of having a Name or Answer property; then you can do:
if(object.Answer == questionComponent)
//do stuff
And ToString does not turn the object into a string. It simply returns a user-defined (if you choose to override) string for the object - for the Ints it is "42", and for bools it is "true" or "false". No conversion occurs.
Based on your edit, it sounds like all you're trying to do is be able to look up some concrete object based on a string that you get from a data file? Couldn't you use a Dictionary for this, as in:
Fruit apple = new Apple();
Fruit orange = new Orange();
Dictionary<string,Fruit> map = new Dictionary<string,Fruit>();
map["apple"] = apple;
map["orange"] = orange;
and then later you can get the user's answer/input:
string input = ...
Fruit result;
if(map.TryGetValue(input, out result)) {
// `fruit` now holds the fruit object the user selected.
} else {
// User input did not correspond to a known fruit.
}
But I'm still not convinced I'm understanding your question properly.
It looks like the range of possible strings is limited, so why not just use identifiers in the form of Enums, which you can parse from the string, and set that identifier into the answers and the fruits?
public enum AnswerType
{
Apple,
Pear,
Banana
}
Store the answers in a dictionary mapping ids to answers (casting enum to int for the key), plus the correct answer's id, and now you can know which answer was picked each time, checking the eaten fruit's id, and if the answer was right.