Searching a Set in Swift - swift

Question

I have something like the following
struct ht : Hashable {
var x : Int
var y : Int
var z : Int
//Edit added following func following Ahmad's comment
var hashValue: Int { return (x+y+z) }
static func == (lhs: ht, rhs: ht) -> Bool
{
return lhs.x == rhs.x
&& lhs.y == rhs.y
&& lhs.z == rhs.z
}
}
let defaultX = 4
let searchForX = 7
//let searchForX = 1000000
var ss : Set<ht> = [ ht(x:1,y:2,z:3), ht(x:4,y:5,z:6), ht(x:7, y:8, z:100), ht(x:9, y:19, z:12)]
Does Swift have LINQ like functionality where I can search the set ss to retrieve the struct that matches searchForX = 7 as shown above to return (7, 8, 100)? If searchForX = 1000000 I want it to return (4, 5, 6), so failing over to returning the value where defaultX = 4
My current code uses loops. In C# you can use LINQ and specify .FirstOrDefault(...).
Is this possible in Swift?
Thank you

Answer 1

Swift isn't really my thing but a ternary operator similar to the code below may move you along.
var answer = ss.first(where: { $0.x == searchForX }) ?? ss.first(where: { $0.x == defaultX })
Regards
Mike

Answer 2

So the quick answer to your question is
let element = ss.first { $0.x == searchForX } ?? ss.first { $0.x == defaultX }
This can be turned a simple extension
extension Sequence {
func first(_ criteria: (Element) -> Bool, orDefault: (Element) -> Bool) -> Element? {
return first(where: criteria) ?? first(where: orDefault)
}
}
let element = ss.first({ $0.x == searchForX }, orDefault: { $0.x == searchForX })
By making this an extension on Sequence, it will work for Arrays and anything that implements Sequence.
If you are concerned about performance you can roll your own.
extension Sequence {
func first(_ criteria: (Element) -> Bool, orDefault: (Element) -> Bool) -> Element? {
var defaultElement: Element?
for element in self {
if criteria(element) { return element }
if criteria(element) { defaultElement = element }
}
return defaultElement
}
}

Answer 3

You could implement your own custom method to do the desired functionality.
First of all, if you would declare a set of custom structs, note that your struct must be Hashable protocol -which means that it implicitly must be Equatable -, thus it would be implemented as follows:
struct MyStruct: Hashable, Equatable {
var x : Int
var y : Int
var z : Int
// Hashable
var hashValue: Int
// Equatable
static func ==(lhs: MyStruct, rhs: MyStruct) -> Bool {
return lhs.x == rhs.x
}
}
So, you could declare a set of MyStruct.
Probably this is not the right way to assign a value to the hashValue, but for the purpose of answering the question I will assign dummy values to them.
For implementing the method for achieving the desired output, I would recommend to declare it in a set extension (if you would let it also functional for arrays, you could declare it as a Collection extension instead), constrained by the set element type:
extension Set where Element == MyStruct {
func firstOrDefault(for expectedXValue: Int, defaultXValue: Int) -> MyStruct? {
// expeccted
if let expected = first(where: { $0.x == expectedXValue }) {
return expected
}
// default
if let defaultValue = first(where: { $0.x == defaultXValue }) {
return defaultValue
}
// neither
return nil
}
}
Note that if there are more than one expected or default x value in the set, it would returns the first matched one.
You would notice that the main functionality of implementing firstOrDefault method is to use first(where:) method (which is similar to what are you looking for), with a little bit of logic to get a -first- default value instead.
Output:
In case of there is an expected object with x = 7:
let mySet: Set<MyStruct> = [MyStruct(x: 1, y: 2, z: 3, hashValue: 101),
MyStruct(x: 4, y: 5, z: 6, hashValue: 102),
MyStruct(x: 7, y: 8, z: 100, hashValue: 103),
MyStruct(x: 9, y: 19, z: 12, hashValue: 104)]
let myObject = mySet.firstOrDefault(for: 7, defaultXValue: 4)
dump(myObject)
/*
▿ Optional(__lldb_expr_187.MyStruct(x: 7, y: 8, z: 9, hashValue: 102))
▿ some: __lldb_expr_187.MyStruct
- x: 7
- y: 8
- z: 9
- hashValue: 102
*/
In case of there is no expected value and the default x = 4:
let mySet2: Set<MyStruct> = [MyStruct(x: 1, y: 2, z: 3, hashValue: 101),
MyStruct(x: 4, y: 5, z: 6, hashValue: 102),
MyStruct(x: 1000, y: 8, z: 100, hashValue: 103),
MyStruct(x: 9, y: 19, z: 12, hashValue: 104)]
let myObject2 = mySet2.firstOrDefault(for: 7, defaultXValue: 4)
dump(myObject2)
/*
▿ Optional(__lldb_expr_249.MyStruct(x: 4, y: 5, z: 6, hashValue: 102))
▿ some: __lldb_expr_249.MyStruct
- x: 4
- y: 5
- z: 6
- hashValue: 102
*/
In case of there is no expected and no default value:
let mySet3: Set<MyStruct> = [MyStruct(x: 1, y: 2, z: 3, hashValue: 101),
MyStruct(x: 1000, y: 5, z: 6, hashValue: 102),
MyStruct(x: 1000, y: 8, z: 100, hashValue: 103),
MyStruct(x: 9, y: 19, z: 12, hashValue: 104)]
let myObject3 = mySet3.firstOrDefault(for: 7, defaultXValue: 4)
dump(myObject3) // - nil