Create a bar chart with iOS Charts.

.swift

    internal func bodyStateBarChartFromDate(fromDate: NSDate = NSDate(timeIntervalSinceReferenceDate: NSTimeInterval(0)), toDate: NSDate = NSDate(), unit: NSCalendarUnit = .Day) -> BarChartView {
    
        print ("start = \(fromDate), end = \(toDate)")
        
        let chartView = BarChartView()
        // Build the chart view data

        let data = buildHeartRateDataFromDate(fromDate, toDate: toDate, unit: unit)
        
        if data.count == 0 {
            return chartView
        }
        
        let chartData: [BarChartDataEntry] = data.map {
            // HAX:(jl) There is a problem where if the bar height is 0 then any bars with
            // non-zero height float about 10px above the x-axis. This work around solves
            // the problem putting in a transparent bar with a height of 10 for zero values.
            // Ref. https://github.com/danielgindi/Charts/issues/947
            BarChartDataEntry(value: Double($0.averageHeartRate), xIndex: $0.index)
        }
        
        var barColors: [UIColor] = []
        for d in data {
//            if d.averageHeartRate == 0 {
//                // HAX:(jl) See HAX comment above.
//                barColors += [UIColor.clearColor()]
//                continue
//            }
            
            switch d.predominantState {
            case .Recovery:
                barColors += [UIColor.rockyRecoveryColor()]
            case .Exercise:
                barColors += [UIColor.rockyExerciseColor()]
            case .Stress:
                barColors += [UIColor.rockyExertionColor()]
            default:
                ()
            }
        }

        // Chart Look and Feel
        
        let xVals: [String] = formatXAxesTimeValues(fromDate.timeUnitsToDate(toDate, unit: .Hour))

        // All three arrays need to have the same number of entries
        assert(xVals.count == data.count)
        assert(xVals.count == barColors.count)
        
        // Create a data set
        let barChartDataSet: BarChartDataSet = BarChartDataSet(yVals: chartData, label: "")
        barChartDataSet.drawValuesEnabled = false
        barChartDataSet.colors = barColors
        
        var barChartDataSets: [BarChartDataSet] = []
        barChartDataSets.append(barChartDataSet)
        
        // Config Look and Feel
        
        chartView.descriptionText = ""
        chartView.drawGridBackgroundEnabled = false
        chartView.drawBordersEnabled = false
        chartView.dragEnabled = false
        chartView.gridBackgroundColor = UIColor.rockyChartLegendColor()
        chartView.pinchZoomEnabled = false
        chartView.drawBordersEnabled = false
        chartView.scaleXEnabled = true
        chartView.scaleYEnabled = false
        chartView.highlightPerTapEnabled = false
        
        let legend = chartView.legend
        legend.enabled = false
        
//        let xAxis = chartView.xAxis
//        xAxis.drawAxisLineEnabled = true
//        xAxis.drawLabelsEnabled = true
//        xAxis.drawGridLinesEnabled = false
//        xAxis.drawLimitLinesBehindDataEnabled = false
//        xAxis.labelPosition = .Bottom
//        xAxis.labelTextColor = UIColor.rockyChartLegendColor()
//        xAxis.avoidFirstLastClippingEnabled = true
        
        let xAxis: ChartXAxis = chartView.xAxis
        xAxis.drawAxisLineEnabled = true
        xAxis.drawLabelsEnabled = true
        xAxis.drawGridLinesEnabled = false
        xAxis.labelTextColor = UIColor.rockyChartLegendColor()
        xAxis.drawLimitLinesBehindDataEnabled = false
        xAxis.labelPosition = .Bottom
        
        let leftAxis = chartView.leftAxis
        leftAxis.enabled = false
        
//        let leftAxis = chartView.leftAxis
//        leftAxis.drawAxisLineEnabled = false
//        leftAxis.drawLabelsEnabled = false
//        leftAxis.drawGridLinesEnabled = false

        let rightAxis = chartView.rightAxis
        rightAxis.drawAxisLineEnabled = false
        rightAxis.drawLabelsEnabled = true
        rightAxis.drawGridLinesEnabled = false
        rightAxis.drawTopYLabelEntryEnabled = true
        rightAxis.startAtZeroEnabled = true
        rightAxis.labelCount = 6
        // rightAxis.axisMaxValue = 120
        rightAxis.axisMinValue = 0
        rightAxis.valueFormatter = NSNumberFormatter()
        rightAxis.valueFormatter!.maximumFractionDigits = 0
        rightAxis.labelTextColor = UIColor.rockyChartLegendColor()
        
        // Assign the chart data last or you need to notificy the chart
        // the data has changed !!!
        
        chartView.data = BarChartData(xVals: xVals, dataSets: barChartDataSets)
        chartView.notifyDataSetChanged()
        
        return chartView
    }