如何统计Swift动态列表中特定属性的数量？以isTaken属性为例

原始数据代码 #

@Published var storedMedicines: [Medicine] = [
    Medicine(Title: "Medicine 1", Description: "Lower blood sugar", date: .init(timeIntervalSince1970: 1664779248), isTaken: false),
    Medicine(Title: "Medicine 1", Description: "Lower blood sugar", date: .init(timeIntervalSince1970: 1664880248), isTaken: false),
    Medicine(Title: "Medicine 1", Description: "Lower blood sugar", date: .init(timeIntervalSince1970: 1664720990), isTaken: false),
    Medicine(Title: "Medicine 1", Description: "Lower blood sugar", date: .init(timeIntervalSince1970: 1664720990), isTaken: false),
]

实现方法 #

方法1：两次filter统计

通过filter分别筛选出isTaken为true和false的元素，再获取对应数量：

let takenCount = storedMedicines.filter { $0.isTaken }.count
let notTakenCount = storedMedicines.filter { !$0.isTaken }.count
print("\(takenCount)个isTaken为true，\(notTakenCount)个isTaken为false")

方法2：单次reduce统计（更高效）

用reduce遍历一次数组同时统计两种状态的数量，避免多次遍历数组，适合元素较多的场景：

let countResult = storedMedicines.reduce((taken: 0, notTaken: 0)) { accumulator, medicine in
    medicine.isTaken 
        ? (taken: accumulator.taken + 1, notTaken: accumulator.notTaken)
        : (taken: accumulator.taken, notTaken: accumulator.notTaken + 1)
}
print("\(countResult.taken)个isTaken为true，\(countResult.notTaken)个isTaken为false")

内容的提问来源于stack exchange，提问作者Gem12345