如何使用每天 1 个单位而不是每个数据点 1 个单位的 Swift 图表创建 x 轴？

Question

我有一个需要时间序列数据的图表。时间序列数据每天最多记录一次，但不定期。即，数据可能如下所示：

1/1, 1500
1/13, 1600
1/14, 1700
2/22, 1800
5/1, 1400

使用图表，我的折线图以每个数据点一个单位填充 x 轴（即，在上面的示例中，x 轴上将有 5 个单位，而不是约 120 天）

如何为范围内的所有日期创建带有单位的 x 轴？

我的图表代码：

    func setChartData(data: ([String], [Double])) {
        var yVals1 = [ChartDataEntry]()
        for i in 0 ..< data.0.count {
            yVals1.append(ChartDataEntry(value: data.1[i], xIndex: i))
        }

        let set1: LineChartDataSet = LineChartDataSet(yVals: yVals1, label: nil)
        set1.axisDependency = .Left 

        set1.setColor(UIColor(red:0.502, green:0.580, blue:0.784, alpha:1.000))
        set1.lineWidth = 2.0
        set1.fillAlpha = 1
        set1.fillColor = UIColor(red:0.502, green:0.580, blue:0.784, alpha:1.000)
        set1.highlightColor = UIColor.whiteColor()
        set1.drawValuesEnabled = false
        set1.drawCirclesEnabled = false
        set1.drawFilledEnabled = true


        var dataSets : [LineChartDataSet] = [LineChartDataSet]()
        dataSets.append(set1)

        let data: LineChartData = LineChartData(xVals: data.0, dataSets: dataSets)
        data.setValueTextColor(UIColor.whiteColor())

        let legend = lineChartView.legend
        legend.enabled = false

        let xAxis = lineChartView.xAxis
        xAxis.drawGridLinesEnabled = false
        xAxis.drawAxisLineEnabled = false
        xAxis.labelPosition = .Bottom

        let rightAxis = lineChartView.rightAxis
        rightAxis.drawAxisLineEnabled = false
        rightAxis.drawLabelsEnabled = false
        rightAxis.drawGridLinesEnabled = false

        let leftAxis = lineChartView.leftAxis
        leftAxis.drawAxisLineEnabled = false
        leftAxis.gridColor = UIColor.blackColor().colorWithAlphaComponent(0.1)
        leftAxis.gridLineWidth = 2


        self.lineChartView.data = data
    }

Answer 1

不是直接传递数据点，而是转换数据点以将所有相关日期包含为 x 值（1 天间隔，即使那一天没有关联的 y 值）并适当填写 y 值，其中它们存在。

1. 构建一个每天包含 1 个元素的 x 值数组
2. 如果那天有值，则将该值添加到 y 值数组。否则将 nil 添加到 y 值数组。

代码：

struct StatsViewModel {

    var exercise: Exercise

    var workoutDates: ([String], [Double?]) {
        if let lastWorkout = exercise.workoutDiary.last, firstWorkout = exercise.workoutDiary.first {
            var dates = [String]()
            var stats = [Double?]()
            let ti:NSTimeInterval = 24*60*60 //one day
            let dateFrom = firstWorkout.date
            let dateTo = lastWorkout.date

            var nextDate =  dateFrom
            let endDate = dateTo.dateByAddingTimeInterval(ti)

            while nextDate.compare(endDate) == NSComparisonResult.OrderedAscending
            {
                dates.append(nextDate.myPrettyString)
                let workout = exercise.workoutDiary.filter { $0.date.myPrettyString == nextDate.myPrettyString }.first
                if let workout = workout {
                    stats.append(Double(workout.totalVolume))
                } else {
                    stats.append(nil)
                }
                nextDate = nextDate.dateByAddingTimeInterval(ti)
            }           
            return (dates, stats)
        }
        return ([], [])
    }
}

从上面生成的数据点创建 ChartDataEntry，占 nil：

var statsViewModel: StatsViewModel!

override func viewDidLoad() {
    setChartData(statsViewModel.workoutDates)
}

func setChartData(data: ([String], [Double?])) {
    var yVals1 = [ChartDataEntry]()
    for i in 0 ..< data.0.count {
        if let yval = data.1[i] {
            yVals1.append(ChartDataEntry(value: yval, xIndex: i))
        }
    }
    let set1: LineChartDataSet = LineChartDataSet(yVals: yVals1, label: nil)
    var dataSets : [LineChartDataSet] = [LineChartDataSet]()
    dataSets.append(set1)

    let data: LineChartData = LineChartData(xVals: data.0, dataSets: dataSets)
    data.setValueTextColor(UIColor.whiteColor())
    ...
}

Answer 2

由于 Chart API 更改，已接受的答案已过时。

ChartDataEntry 值必须由 (x, y): (Double, Double) 组成，并且不能 包含String，尽管您使用自定义显示格式化程序来显示数据。

设置一个实现IAxisValueFormatter 协议的MonthTimeXAxisValueFormatter 以返回String 值：

class MonthTimeXAxisValueFormatter: IAxisValueFormatter {
  func stringForValue(_ value: Double, axis: AxisBase?) -> String {
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "dd MMM"
    let timeStamp = Date(timeIntervalSince1970: value)
    return dateFormatter.string(from: timeStamp)
  }
}

// Setup the x-axis with this formatter.
lineChart.xAxis.valueFormatter = MonthTimeXAxisValueFormatter()

此处的 x 值应生成为：

  func chartDataPoints(from xYValues: [Date: Double]) -> [ChartDataEntry] {
    assert(!xYValues.isEmpty)
    var dataPoints: [ChartDataEntry] = []
    var startDate = xYValues.keys.sorted(by: <).first!
    let endDate = xYValues.keys.sorted(by: >).first!

    repeat {
      guard let yValue = xYValues[startDate] else {
        startDate = startDate.advanced(by: TimeInterval(24 * 60 * 60))
        continue
      }
      dataPoints.append(ChartDataEntry(x: Double(startDate.timeIntervalSince1970), y: yValue))
      startDate = startDate.advanced(by: TimeInterval(24 * 60 * 60))
    } while startDate <= endDate
    return dataPoints
  }