U ovom vodiču naučit ćete o skupovima, stvaranju skupova, njihovom mijenjanju i nekim uobičajenim operacijama u skupovima.
U prethodnom članku Swift Arrays saznali smo o stvaranju niza koji može sadržavati više vrijednosti na uređenom popisu.
Ali, ako moramo biti sigurni da popis može sadržavati vrijednost samo jednom, koristimo skup u Swiftu.
Što je set?
Set je jednostavno spremnik koji može sadržavati višestruku vrijednost vrste podataka na neuređenom popisu i osigurava jedinstveni element u spremniku (tj. Svaki se podatak pojavljuje samo jednom).
Neuređeni popis znači da nećete dobiti elemente istim redoslijedom kao što ste definirali stavke u skupu.
Glavna prednost korištenja skupova nad nizovima je kada trebate osigurati da se stavka pojavi samo jednom i kada redoslijed stavki nije važan.
Vrijednosti pohranjene u skupu moraju biti raspršive . To znači da mora osigurati svojstvo hashValue. To je važno jer su skupovi neuređeni i koristi hashValue koji se koristi za pristup elementima skupova.
Sve Swift je osnovna tipa (kao što su String, Int, Doublei Bool) su hashable po defaultu, a može se koristiti kao postavljenih tipova vrijednosti. Međutim, također možete stvoriti svoj hashable type u Swiftu koji se može pohraniti u set.
Kako prijaviti set u Swiftu?
Možete stvoriti prazan skup tako što ćete odrediti vrstu kao Set, a zatim vrstu podataka u koju može spremiti.
Primjer 1: Deklaracija praznog skupa
let emptyIntSet:Set = () print(emptyIntSet)
ILI
let emptyIntSet:Set = Set() print(emptyIntSet)
Kada pokrenete program, izlaz će biti:
()
U gore navedenom programu proglasili smo konstantu tipa emptyIntSet Setkoja može pohraniti više vrijednosti cijelih brojeva i inicijalizirati s 0 vrijednosti.
Budući da je Swift jezik zaključivanja tipa, također možete stvoriti skup izravno bez navođenja tipa podataka, ali ga morate inicijalizirati s nekim vrijednostima kako bi kompajler mogao zaključiti o njegovom tipu kao:
Primjer 2: Deklariranje skupa s nekim vrijednostima
let someIntSet:Set = (1, 2, 3, 4, 5, 6, 7, 8, 9) print(someIntSet)
Kada pokrenete program, izlaz će biti:
(2, 4, 9, 5, 6, 7, 3, 1, 8)
U gore navedenom programu proglasili smo konstantu someIntSet koja može pohraniti skupove Integer-a bez eksplicitne specifikacije tipa. Međutim, moramo :Setdefinirati kada definiramo varijablu, inače će Swift stvoriti niz za nas.
Također, kao nizovi, inicijalizirali smo skup s vrijednostima 1, 2, 3, 4, 5, 6, 7, 8, 9 pomoću ()zagrada.
Kao što ste naučili, kada pokušate ispisati vrijednosti unutar skupa kao print(someIntSet), dobit ćete rezultate drugačijim redoslijedom nego što ste definirali stavke u skupu, jer pohranjuje vrijednost bez definiranog redoslijeda. Stoga se svaki put kada pristupite redoslijedu promijeni.
Primjer 3: Deklariranje skupa dvostrukim vrijednostima
let someStrSet:Set = ("ab","bc","cd","de","ab") print(someStrSet)
Kada pokrenete program, izlaz će biti:
("de", "ab", "cd", "bc")
U gornjem programu definirali smo dupliciranu vrijednost ab u skupu. I. kada pokušavamo pristupiti vrijednosti unutar skupa pomoću print(someStrSet), duplikata se vrijednost automatski uklanja iz skupa. Stoga set jamči jedinstvene elemente / vrijednosti unutar sebe.
Skup također možete prijaviti s vlastitim prilagođenim tipom Hashable u Swiftu. Da biste saznali više, posjetite Swift Hashable.
Kako pristupiti postavljenim elementima u Swiftu?
Ne možete pristupiti elementima skupa koristeći sintaksu indeksa kao nizove. To je zato što su skupovi neuređeni i nemaju indekse za pristup elementima.
Dakle, morate pristupiti skupu pomoću njegovih metoda i svojstava ili pomoću petlji za ulazak.
Primjer 4: Pristup elementima skupa
var someStrSet:Set = ("ab", "bc", "cd", "de") for val in someStrSet ( print(val) )
Kada pokrenete program, izlaz će biti:
de ab cd bc
In the above program, we get the val in different order than elements of a set because sets are unordered unlike arrays.
You can also access element of a set directly removing the value from the set as below:
Example 5: Accessing elements of a set using remove()
var someStrSet:Set = ("ab", "bc", "cd", "de") let someVal = someStrSet.remove("cd") print(someVal) print(someStrSet)
When you run the program, the output will be:
Optional("cd") ("de", "ab", "bc")
In the above program, you can see the remove method returns an optional string. Therefore, it's recommended you to do optional handling as below. To learn more about optionals, visit Swift Optionals.
Example 6: Optional handling for remove()
var someStrSet:Set = ("ab", "bc", "cd", "de") if let someVal = someStrSet.remove("cd") ( print(someVal) print(someStrSet) ) else ( print("cannot find element to remove") )
When you run the program, the output will be:
cd ("de", "ab", "bc")
How to add new element in a set?
You can add a new element to a set using insert() method in Swift.
Example 7: Add new element using insert()
var someStrSet:Set = ("ab", "bc", "cd", "de") someStrSet.insert("ef") print(someStrSet)
When you run the program, the output will be:
("ab", "de", "cd", "ef", "bc")
In the above program, we used the set's insert() method to add a new element to a set. Since, sets are unordered, the position of the inserted element isn't known.
Set Operations
Another main advantage of using Sets is you can perform set operations such as combining two sets together, determining which values two sets have in common etc. This operations are similar to the Set operation in Mathematics.
1. Union
The union of two sets a and b is the set of elements which are in a, or b, or in both a and b.
let a: Set = (1, 3, 5, 7, 9) let b: Set = (0, 2, 4, 6, 8) print(a.union(b))
When you run the above program, the output will be:
(8, 2, 9, 4, 5, 7, 6, 3, 1, 0)
2. Intersection
The intersection of two sets a and b is the set that contains all elements of a that also belong to b.
let a: Set = (1, 3, 5, 7, 9) let b: Set = (0, 3, 7, 6, 8) print(a.intersection(b))
When you run the above program, the output will be:
(7, 3)
Therefore, print(a.intersection(b)) outputs a new set with values (7, 3) that are common in both a and b.
3. Subtracting
The subtraction of two sets a and b is the set that contains all elements of a but removing the elements that also belong to b.
let a: Set = (1, 3, 5, 7, 9) let b: Set = (0, 3, 7, 6, 8) print(a.subtracting(b))
When you run the above program, the output will be:
(5, 9, 1)
Therefore, print(a.subtracting(b)) outputs a new set with values (5, 9, 1).
4. Symmetric Difference
The symmetric difference of two sets a and b is the set that contains all elements which are in either of the sets but not in both of them.
let a: Set = (1, 3, 5, 7, 9) let b: Set = (0, 3, 7, 6, 8) print(a.symmetricDifference(b))
When you run the above program, the output will be:
(5, 6, 8, 0, 1, 9)
Therefore, print(a.symmetricDifference(b)) outputs a new set with values (5, 6, 8, 0, 1, 9).
Set Membership and Equality Operations
Set Equality
You can use == operator to check whether two sets contains same elements or not. It returns true if two sets contains same elements otherwise returns false.
Example 5: Set equality operations
let a: Set = (1, 3, 5, 7, 9) let b: Set = (0, 3, 7, 6, 8) let c:Set = (9, 7, 3, 1, 5) if a == b ( print("a and b are same") ) else ( print("a and b are different") ) if a == c ( print("a and c are same") ) else ( print("a and c are different") )
When you run the above program, the output will be:
a and b are different a and c are same
Set membership
You can also check relationship between two sets using the following methods:
isSubset(of:)This method determines whether all of the values of a set are contained in the specified set.isSuperset(of:)This method determines whether a set contains all of the values in a specified setisStrictSubset(of:) orisStrictSuperset(of:): This method determines whether a set is a subset or superset, but not equal to, a specified set.isDisjoint(with:)This method determines whether two sets have no values in common.
Example 6: Set membership operations
let a: Set = (1, 3, 5, 7, 9) let b: Set = (0, 3, 1, 7, 6, 8, 9, 5) print("isSubset:", a.isSubset(of: b)) print("isSuperset:", b.isSuperset(of: a)) print("isStrictSubset:", a.isStrictSubset(of: b)) print("isDisjointWith:", a.isDisjoint(with: b))
When you run the above program,the output will be:
isSubset: true isSuperset: true isStrictSubset: true isDisjointWith: false
Let's analyze methods used inside the print statement below:
isSubsetreturnstruebecause the set b contains all the elements in aisSupersetreturntruebecause b contains all of the values of a.isStrictSubsetreturnstruebecause set b contains all the element in a and both sets are not equal.isDisjointWithreturnsfalsebecause a and b have some values in common.
Some helpful built in Set functions & properties
1. isEmpty
This property determines if a set is empty or not. It returns true if a set does not contain any value otherwise returns false.
Example 7: How isEmpty works?
let intSet:Set = (21, 34, 54, 12) print(intSet.isEmpty)
When you run the program, the output will be:
false
2. first
This property is used to access first element of a set.
Example 8: How first works?
let intSet = (21, 34, 54, 12) print(intSet.first)
When you run the program, the output will be:
Optional(54)
Since set is an unordered collection, the first property does not guarantee the first element of the set. You may get other value than 54.
Similarly, you can use last property to access last element of a set.
3. insert
The insert function is used to insert/append element in the set.
Example 9: How insert works?
var intSet:Set = (21, 34, 54, 12) intSet.insert(50) print(intSet)
When you run the program, the output will be:
(54, 12, 50, 21, 34)
4. reversed
This function returns the elements of a set in reverse order.
Example 10: How reversed() works?
var intSet:Set = (21, 22, 23, 24, 25) print(intSet) let reversedSet = intSet.reversed() print(reversedSet)
When you run the program, the output will be:
(22, 23, 21, 24, 25) (25, 24, 21, 23, 22)
5. count
This property returns the total number of elements in a set.
Example 11: How count works?
let floatSet:Set = (10.2, 21.3, 32.0, 41.3) print(floatSet.count)
When you run the program, the output will be:
4
6. removeFirst
This function removes and returns the first value from the set.
Example 12: How removeFirst works?
var strSet:Set = ("ab", "bc", "cd", "de") let removedVal = strSet.removeFirst() print("removed value is (removedVal)") print(strSet)
When you run the program, the output will be:
removed value is de ("ab", "cd", "bc")
Slično tome, možete koristiti i removeAllfunkciju za pražnjenje seta.
