如何在Swift中按数组元素分组

斯威夫特4： 从Swift 4开始，此功能已添加到标准库中。您可以这样使用它：

Dictionary(grouping: statEvents, by: { $0.name }) [ "dinner": [ StatEvents(name: "dinner", date: "01-01-2015", hours: 1), StatEvents(name: "dinner", date: "01-01-2015", hours: 1), StatEvents(name: "dinner", date: "01-01-2015", hours: 1) ], "lunch": [ StatEvents(name: "lunch", date: "01-01-2015", hours: 1), StatEvents(name: "lunch", date: "01-01-2015", hours: 1) ] 斯威夫特3： public extension Sequence { func group<U: Hashable>(by key: (Iterator.Element) -> U) -> [U:[Iterator.Element]] { var categories: [U: [Iterator.Element]] = [:] for element in self { let key = key(element) if case nil = categories[key]?.append(element) { categories[key] = [element] } } return categories } } 不幸的是，append上面的函数复制了基础数组，而不是对其进行适当的突变，这将是更好的选择。这会导致很大的减速。您可以通过使用引用类型包装器解决该问题：

class Box { var value: A init(_ val: A) { self.value = val } }

public extension Sequence { func group<U: Hashable>(by key: (Iterator.Element) -> U) -> [U:[Iterator.Element]] { var categories: [U: Box<[Iterator.Element]>] = [:] for element in self { let key = key(element) if case nil = categories[key]?.value.append(element) { categories[key] = Box([element]) } } var result: [U: [Iterator.Element]] = Dictionary(minimumCapacity: categories.count) for (key,val) in categories { result[key] = val.value } return result } } 即使您两次遍历最终字典，此版本在大多数情况下仍比原始字典快。

斯威夫特2： public extension SequenceType {

/// Categorises elements of self into a dictionary, with the keys given by keyFunc

func categorise(@noescape keyFunc: Generator.Element -> U) -> [U:[Generator.Element]] { var dict: [U:[Generator.Element]] = [:] for el in self { let key = keyFunc(el) if case nil = dict[key]?.append(el) { dict[key] = [el] } } return dict } } 在您的情况下，您可以keyFunc使用以下名称返回“ keys” ：

currentStat.statEvents.categorise { $0.name } [
dinner: [ StatEvents(name: "dinner", date: "01-01-2015", hours: 1), StatEvents(name: "dinner", date: "01-01-2015", hours: 1), StatEvents(name: "dinner", date: "01-01-2015", hours: 1) ], lunch: [ StatEvents(name: "lunch", date: "01-01-2015", hours: 1), StatEvents(name: "lunch", date: "01-01-2015", hours: 1) ] ] 因此，您将获得一个字典，其中每个键都是一个名称，每个值都是具有该名称的StatEvents的数组。

斯威夫特1 func categorise<S : SequenceType, U : Hashable>(seq: S, @noescape keyFunc: S.Generator.Element -> U) -> [U:[S.Generator.Element]] { var dict: [U:[S.Generator.Element]] = [:] for el in seq { let key = keyFunc(el) dict[key] = (dict[key] ?? []) + [el] } return dict }

categorise(currentStat.statEvents) { $0.name } 给出输出：

extension StatEvents : Printable { var description: String { return "(self.name): (self.date)" } } print(categorise(currentStat.statEvents) { $0.name }) [ dinner: [ dinner: 01-01-2015, dinner: 01-01-2015, dinner: 01-01-2015 ], lunch: [ lunch: 01-01-2015, lunch: 01-01-2015 ] ]