Charts: LineChartView with a line that goes backwards

[davidebalistreri]

What did you do?

I need to draw the FVC graph (flow-volume) for a macOS app.

The graph should represent the loop-curve which measures the amount (volume) and speed (flow) of the air that was exhaled and inhaled by a patient during a breathing test.

Example:

I managed to draw the exhalation phase correctly and effortlessly (in the example it starts from 0 and it goes forward and upward, reaching the Peak expiratory flow at 12 liters per seconds, then slowly decreases until it almost reaches the 6 liters maximum volume).

What did you expect to happen?

After the exhalation phase, the graph should draw a line that goes backwards and below the x-axis, for the inhalation phase (in the example it starts from almost 6 liters of volume, goes backwards, reaches the -7 liters per seconds flow, then reconnects at 0).

What happened instead?

During the inhalation phase the values go backwards. Sometimes one value is drawn properly, sometimes not, either way when a second value is passed the graph ceases to work, and it removes all drawn lines (I think it crashes).

I tried to simulate this behavior in the ChartsDemo-macOS app, by creating a simple LineChartView with these values:

x: 0, y: 0
x: 2, y: 2
x: 4, y: 4
x: 2, y: 6
x: 0, y: 8

The fourth value (x: 2, y: 6) isn't drawn at all.

The fifth value (x: 0, y: 8) makes the app crash:

Fatal error: Can't form Range with upperBound < lowerBound

Charts Environment

Charts version/Branch/Commit Number: 3.2.2 (branch: master, commit: 5d0b99adb860406059e42149520ce9c0cb847feb)
Xcode version: 10.1, 10.2
Swift version: 4.2
Platform(s) running Charts: macOS
macOS version running Xcode: 10.14.3 (18D109), 10.14.4 (18E226)

Demo Project

Demo project with the values described above:
ChartsDemo-macOS-linebug.zip

[lucasmpaim]

Hi,

I get this error too, the error that is occurring is because your X values is not sorted on your dataset,
this is a restriction of library in both plataforms.

Something like this:

entries.sort(by: { $0.x < $1.x })

will fix the error

[davidebalistreri]

Hi @lucasmpaim, and thank you for your feedback!

Unfortunately I shouldn't sort the values, otherwise I'll get a wrong graph:

Anyway I managed to achieve my goal by manually setting the proper "min" and "max" values in the BarLineScatterCandleBubbleRenderer.XBounds class:

This is the resulting graph, representing the input values just as expected:

I don't quite understand how the XBounds class calculates its "min" and "max" values, but if we enhance that we can support datasets that go backwards.

Let me know if I can help!

[liuxuan30]

sees we can close now

[davidebalistreri]

The bug is still there, but thank you anyway.

[TerletskyIgor]

I had the same problem.
How I solved this problem:

• I needed to keep the order of my points.
• I had two arrays of points.
• I created a dictionary. In which the first array was keys, the second array was values.

Then I sorted the dictionary by keys. It solved this problem.

//your value
let l0 = [Double]()
let l1 = [Double]()

var temp = [Double: Double]()

 for i in 0..<l0.count {
    let key = l0[i]
    let value = l1[i]
    temp[key] = value
}
temp.sorted {$0.key < $1.key}

After that, there was a problem that the function graph was filled in and inside.
To fix this, I added:

let line1 = LineChartDataSet(entries: lineChartEntry1, label: nil)
line1.drawCirclesEnabled = true // Default value
line1.colors = [UIColor (red: CGFloat (0/255), green: CGFloat (0/255), blue: CGFloat (0/255), alpha: 0)]

When you set the color to transparent, you will get your function graph that won`t be filled inside.
In my case there was a lot of point and all drawCircles seem like a solid line.

I know that this is not the best solution =)