我可能有一个像下面这样的数组:
[1, 4, 2, 2, 6, 24, 15, 2, 60, 15, 6]
或者,实际上,任何类似类型的数据部分的序列。我要做的是确保每个相同的元素只有一个。例如,上面的数组将变成:
[1, 4, 2, 6, 24, 15, 60]
请注意,删除了2、6和15的重复项,以确保每个相同的元素中只有一个。Swift是否提供了一种容易做到这一点的方法,还是我必须自己做?
我可能有一个像下面这样的数组:
[1, 4, 2, 2, 6, 24, 15, 2, 60, 15, 6]
或者,实际上,任何类似类型的数据部分的序列。我要做的是确保每个相同的元素只有一个。例如,上面的数组将变成:
[1, 4, 2, 6, 24, 15, 60]
请注意,删除了2、6和15的重复项,以确保每个相同的元素中只有一个。Swift是否提供了一种容易做到这一点的方法,还是我必须自己做?
当前回答
下面是SequenceType上的一个类别,它保留了数组的原始顺序,但使用Set来进行contains查找,以避免数组的contains(_:)方法上的O(n)代价。
public extension Sequence where Element: Hashable {
/// Return the sequence with all duplicates removed.
///
/// i.e. `[ 1, 2, 3, 1, 2 ].uniqued() == [ 1, 2, 3 ]`
///
/// - note: Taken from stackoverflow.com/a/46354989/3141234, as
/// per @Alexander's comment.
func uniqued() -> [Element] {
var seen = Set<Element>()
return self.filter { seen.insert($0).inserted }
}
}
如果你不是Hashable或Equatable,你可以传入一个谓词来进行相等性检查:
extension Sequence {
/// Return the sequence with all duplicates removed.
///
/// Duplicate, in this case, is defined as returning `true` from `comparator`.
///
/// - note: Taken from stackoverflow.com/a/46354989/3141234
func uniqued(comparator: @escaping (Element, Element) throws -> Bool) rethrows -> [Element] {
var buffer: [Element] = []
for element in self {
// If element is already in buffer, skip to the next element
if try buffer.contains(where: { try comparator(element, $0) }) {
continue
}
buffer.append(element)
}
return buffer
}
}
现在,如果你没有Hashable,但是是Equatable,你可以使用这个方法:
extension Sequence where Element: Equatable {
/// Return the sequence with all duplicates removed.
///
/// i.e. `[ 1, 2, 3, 1, 2 ].uniqued() == [ 1, 2, 3 ]`
///
/// - note: Taken from stackoverflow.com/a/46354989/3141234
func uniqued() -> [Element] {
return self.uniqued(comparator: ==)
}
}
最后,你可以添加一个unique的关键路径版本,如下所示:
extension Sequence {
/// Returns the sequence with duplicate elements removed, performing the comparison using the property at
/// the supplied keypath.
///
/// i.e.
///
/// ```
/// [
/// MyStruct(value: "Hello"),
/// MyStruct(value: "Hello"),
/// MyStruct(value: "World")
/// ].uniqued(\.value)
/// ```
/// would result in
///
/// ```
/// [
/// MyStruct(value: "Hello"),
/// MyStruct(value: "World")
/// ]
/// ```
///
/// - note: Taken from stackoverflow.com/a/46354989/3141234
///
func uniqued<T: Equatable>(_ keyPath: KeyPath<Element, T>) -> [Element] {
self.uniqued { $0[keyPath: keyPath] == $1[keyPath: keyPath] }
}
}
你可以把这两个都放在你的应用程序中,Swift会根据你的序列的迭代器选择正确的一个。元素类型。
对于El Capitan,您可以扩展此方法以包括多个键盘,如下所示:
/// Returns the sequence with duplicate elements removed, performing the comparison using the property at
/// the supplied keypaths.
///
/// i.e.
///
/// ```
/// [
/// MyStruct(value1: "Hello", value2: "Paula"),
/// MyStruct(value1: "Hello", value2: "Paula"),
/// MyStruct(value1: "Hello", value2: "Bean"),
/// MyStruct(value1: "World", value2: "Sigh")
/// ].uniqued(\.value1, \.value2)
/// ```
/// would result in
///
/// ```
/// [
/// MyStruct(value1: "Hello", value2: "Paula"),
/// MyStruct(value1: "Hello", value2: "Bean"),
/// MyStruct(value1: "World", value2: "Sigh")
/// ]
/// ```
///
/// - note: Taken from stackoverflow.com/a/46354989/3141234
///
func uniqued<T: Equatable, U: Equatable>(_ keyPath1: KeyPath<Element, T>, _ keyPath2: KeyPath<Element, U>) -> [Element] {
self.uniqued {
$0[keyPath: keyPath1] == $1[keyPath: keyPath1] && $0[keyPath: keyPath2] == $1[keyPath: keyPath2]
}
}
但是(恕我直言)你最好把你自己的block传递给self.unique。
其他回答
为此,我做了一个尽可能简单的扩展。
extension Array where Element: Equatable {
func containsHowMany(_ elem: Element) -> Int {
return reduce(0) { $1 == elem ? $0 + 1 : $0 }
}
func duplicatesRemoved() -> Array {
return self.filter { self.containsHowMany($0) == 1 }
}
mutating func removeDuplicates() {
self = self.duplicatesRemoved(()
}
}
您可以使用duplicatesRemoved()来获取一个新数组,它的重复元素将被删除,或者使用removeduplicate()来改变自身。看到的:
let arr = [1, 1, 1, 2, 2, 3, 4, 5, 6, 6, 6, 6, 6, 7, 8]
let noDuplicates = arr.duplicatesRemoved()
print(arr) // [1, 1, 1, 2, 2, 3, 4, 5, 6, 6, 6, 6, 6, 7, 8]
print(noDuplicates) // [1, 2, 3, 4, 5, 6, 7, 8]
arr.removeDuplicates()
print(arr) // [1, 2, 3, 4, 5, 6, 7, 8]
这只是一个非常简单和方便的实现。具有相等元素的数组扩展中的计算属性。
extension Array where Element: Equatable {
/// Array containing only _unique_ elements.
var unique: [Element] {
var result: [Element] = []
for element in self {
if !result.contains(element) {
result.append(element)
}
}
return result
}
}
首先将数组的所有元素添加到NSOrderedSet中。 这将删除数组中的所有重复项。 再次将这个orderedset转换为一个数组。
做……
例子
let array = [1,1,1,1,2,2,2,2,4,6,8]
let orderedSet : NSOrderedSet = NSOrderedSet(array: array)
let arrayWithoutDuplicates : NSArray = orderedSet.array as NSArray
输出arraywithoutduplates - [1,2,4,6,8]
这里我对对象做了O(n)解。不是少行解决方案,而是……
struct DistinctWrapper <T>: Hashable {
var underlyingObject: T
var distinctAttribute: String
var hashValue: Int {
return distinctAttribute.hashValue
}
}
func distinct<S : SequenceType, T where S.Generator.Element == T>(source: S,
distinctAttribute: (T) -> String,
resolution: (T, T) -> T) -> [T] {
let wrappers: [DistinctWrapper<T>] = source.map({
return DistinctWrapper(underlyingObject: $0, distinctAttribute: distinctAttribute($0))
})
var added = Set<DistinctWrapper<T>>()
for wrapper in wrappers {
if let indexOfExisting = added.indexOf(wrapper) {
let old = added[indexOfExisting]
let winner = resolution(old.underlyingObject, wrapper.underlyingObject)
added.insert(DistinctWrapper(underlyingObject: winner, distinctAttribute: distinctAttribute(winner)))
} else {
added.insert(wrapper)
}
}
return Array(added).map( { return $0.underlyingObject } )
}
func == <T>(lhs: DistinctWrapper<T>, rhs: DistinctWrapper<T>) -> Bool {
return lhs.hashValue == rhs.hashValue
}
// tests
// case : perhaps we want to get distinct addressbook list which may contain duplicated contacts like Irma and Irma Burgess with same phone numbers
// solution : definitely we want to exclude Irma and keep Irma Burgess
class Person {
var name: String
var phoneNumber: String
init(_ name: String, _ phoneNumber: String) {
self.name = name
self.phoneNumber = phoneNumber
}
}
let persons: [Person] = [Person("Irma Burgess", "11-22-33"), Person("Lester Davidson", "44-66-22"), Person("Irma", "11-22-33")]
let distinctPersons = distinct(persons,
distinctAttribute: { (person: Person) -> String in
return person.phoneNumber
},
resolution:
{ (p1, p2) -> Person in
return p1.name.characters.count > p2.name.characters.count ? p1 : p2
}
)
// distinctPersons contains ("Irma Burgess", "11-22-33") and ("Lester Davidson", "44-66-22")
斯威夫特4
public extension Array where Element: Hashable {
func uniqued() -> [Element] {
var seen = Set<Element>()
return filter{ seen.insert($0).inserted }
}
}
每次尝试插入也将返回一个元组:(插入:Bool, memberAfterInsert: Set.Element)。见文档。
使用返回值意味着我们可以避免进行多个循环,因此这是O(n)。