Swift reduce函数问题

Question

我有一组心率。我只想得到最近5分钟的平均心率。(数组包含超过一小时的心率)。

class HeartRate
{
    var hr = 0
    var date : Date?
}

var arrHeartRate = [HeartRate]()
let minDate = Date().addingTimeInterval(-300) //get 5min before time
var avgHR = self.arrHeartRate.filter { (Item) -> Bool in
                return Item.date! > minDate
            }.reduce(0) { (res, item) -> Result<Any, <#Error: Error#>> in
                return res
            }

Answer 1

下面是一些代码，它是不同的stackoverflow答案的聚合。

class HeartRate
{
    var hr = 0
    var date: Date?
}

extension Collection where Iterator.Element == HeartRate, Index == Int {
    /// Returns the average of all elements in the array
    var average: Double {
        return isEmpty ? 0 : Double(reduce(0) { $0 + $1.hr }) / Double(endIndex-startIndex)
    }
}

var arrHeartRate = [HeartRate(), HeartRate()]
let minDate = Date().addingTimeInterval(-300) //get 5min before time
let rateInLast5Min = arrHeartRate.filter {
    guard let date = $0.date else { return false }
    return date > minDate
}
var avgHR = rateInLast5Min.average

Answer 2

您可以在两个步骤中进行过滤和缩减。首先，获取时间范围内的心率数组

let filtered = arrHeartRate.filter{$0.date ?? Date() > minDate}

或者进行一些调整以从已过滤的数组中排除nil date

let filtered = arrHeartRate.filter{$0.date ?? Date().addingTimeInterval(-500) > minDate}

然后计算平均值和收益率

return Double(filtered.reduce(0){$0 + $1.hr}) / Double(filtered.count)

Answer 3

我还没有运行它，但经过一些调整应该是您正在寻找的

    let rateInLast5Min = arrHeartRate.filter({ 0$.date! > minDate  })
let hours = rateInLast5Min.map{ return $0.hr }.reduce(0, +)
let average = Double(hours)/Double(rateInLast5Min.count)