Howto make automatic labels of the left axis be a multiple of some value

[bairog]

Hello.
I need to make automatic labels of the left axis be a multiple of 125. And ensure horizontal gridlines to be drawn for every label.
So that my chart would look something like this (depending on the actual Y values):

1.png (48.39 KiB) Viewed 76811 times

2.png (51.56 KiB) Viewed 76811 times

[Christopher]

Hello,

I think this does it for you:

Code: Select all

        public Form1()
        {
            InitializeComponent();

            var line1 = new Line(tChart1.Chart);
            var line2 = new Line(tChart1.Chart);

            var rnd = new Random();
            var max = 900;

            for (int i = 0; i < 50; i++)
            {
                line1.Add(rnd.Next(max));
                line2.Add(rnd.Next(max));
            }

            tChart1.Axes.Left.Increment = 125;
            tChart1.Axes.Left.Labels.Separation = 1;
            tChart1.Axes.Left.Grid.DrawEvery = 1;
            tChart1.Axes.Left.AutomaticMinimum = false;
            tChart1.Axes.Left.Minimum = 0;
            tChart1.Axes.Left.GetAxisDrawLabel += Left_GetAxisDrawLabel;
        }

        private void Left_GetAxisDrawLabel(object sender, GetAxisDrawLabelEventArgs e)
        {
            e.DrawLabel = e.LabelValue % 125 == 0;
        }

Try changing the value of 'max'.

[bairog]

Thank you. That is exactly what I need. Only one question left: what does tChart1.Axes.Left.Labels.Separation = 1; stand for? I see no changes on a chart when adjusting that value (I've tried 2, 3, 5 and 10).

[Christopher]

Hello,

in theory it:

Screenshot from 2023-08-01 15-45-53.png (17.83 KiB) Viewed 76801 times

but it doesn't seem to work very well. What does work is setting max to a high value (e.g. 9000) and setting Separation to 0—here we can see that it leaves no minimum distance, as it should.

[bairog]

I guess you have a TeeChart.xml file. Could you share it so I don't have to go online every time I need a property description. Thank you.

[Christopher]

There's a Steema.TeeChart.chm file shipped in the TeeChart NuGet packages which has the xml documentation compiled into it. This is what we would suggest you use for 'offline' API documentation.

Screenshot from 2023-08-02 09-46-43.png (102.4 KiB) Viewed 76764 times

[bairog]

But I would like to see function/property description right into IntelliSense. Could you share TeeChart.xml please.

[bairog]

I have done further testing and found that your code does not always work correctly. I you change 125 to 350 and set max = 8000 - it is ok:

Безымянный.png (74.46 KiB) Viewed 76762 times

But you set max = 9000 (and more) - most labels are not multiples of 350:

Безымянный1.png (64.71 KiB) Viewed 76762 times

I've expected auto labels to be set to a multiple of 350 (for example 0, 1750, 3500, 5250, 7000 and 8750). Are there any workarounds?

[Christopher]

Hello,

for finer control, you can use the GetNextAxisLabel event, e.g.

Code: Select all

        const int _increment = 350;
        const int _max = 20000;

        public Form1()
        {
            InitializeComponent();

            var line1 = new Line(tChart1.Chart);
            var line2 = new Line(tChart1.Chart);

            var rnd = new Random();

            for (int i = 0; i < 50; i++)
            {
                line1.Add(rnd.Next(_max));
                line2.Add(rnd.Next(_max));
            }

            tChart1.Axes.Left.Increment = _increment;
            tChart1.Axes.Left.Labels.Separation = 1;
            tChart1.Axes.Left.Grid.DrawEvery = 1;
            tChart1.Axes.Left.AutomaticMinimum = false;
            tChart1.Axes.Left.Minimum = 0;
            tChart1.GetNextAxisLabel += TChart1_GetNextAxisLabel;
        }

        protected override void OnResize(EventArgs e)
        {
            base.OnResize(e);
            tChart1.Header.Text = $"v.{Utils.Version}, size: {tChart1.Height}x{tChart1.Width}, increment: {_increment}, max: {_max}";
        }

        private void TChart1_GetNextAxisLabel(object sender, GetNextAxisLabelEventArgs e)
        {
            var multiplier = Utils.Round(tChart1.Axes.Left.Maximum / _increment / 10);

            int GetValue(int index)
            {
                return _increment * multiplier * index;
            }
            if (sender == tChart1.Axes.Left)
            {
                e.Stop = false;
                switch (e.LabelIndex)
                {
                    case 0: e.LabelValue = 0; break;
                    case 1: e.LabelValue = GetValue(1); break;
                    case 2: e.LabelValue = GetValue(2); break;
                    case 3: e.LabelValue = GetValue(3); break;
                    case 4: e.LabelValue = GetValue(4); break;
                    case 5: e.LabelValue = GetValue(5); break;
                    case 6: e.LabelValue = GetValue(6); break;
                    case 7: e.LabelValue = GetValue(7); break;
                    case 8: e.LabelValue = GetValue(8); break;
                    case 9: e.LabelValue = GetValue(9); break;
                    default: e.Stop = true; break;
                }
            }
        }

Screenshot from 2023-08-03 09-50-40.png (261.52 KiB) Viewed 76736 times

I'm working on getting the xml file to you and will do so when I can.

[Christopher]

A more generic solution would be:

Code: Select all

        private void TChart1_GetNextAxisLabel(object sender, GetNextAxisLabelEventArgs e)
        {
            var max_labels = 20;
            var num = Utils.Round(_max / _increment);
            num = num >= max_labels ? max_labels : num;
            var multiplier = Utils.Round(_max / _increment / num);

            int GetValue(int index)
            {
                return _increment * multiplier * index;
            }

            if (sender == tChart1.Axes.Left)
            {
                e.Stop = false;

                if(e.LabelIndex <= num)
                {
                    e.LabelValue = GetValue(e.LabelIndex);
                }
                else 
                {
                    e.Stop = true;
                }
            }
        }

Screenshot from 2023-08-03 10-34-03.png (265.58 KiB) Viewed 76731 times

[Christopher]

But I would like to see function/property description right into IntelliSense. Could you share TeeChart.xml please.

I've uploaded new NuGet packages containing the necessary xml documentation comments—they are only needed in .NET Framework, according to my tests, as Visual Studio is somehow able to read these comments directly from .NET Core assemblies without the need for the xml file.

[bairog]

A more generic solution would be:

Your code is not working very well when _max / _increment is close to a multiple of max_labels but is slightly less.
In your specific example (max_labels = 20 and _increment = 175) you can just set _max = 13900 (13900 / 175 = 79.428) and get the following picture (there is a big gap between the last label and left axis actual maximum):

Безымянный.png (74.38 KiB) Viewed 76702 times

I have tested some workarounds and the best I have come up with is changing _multiplier formula from Utils.Round(_max / _increment / _num) to (Int32)Math.Round((Double)_max / _increment / _num). With this approach, a greater multiplier is chosen in 50% cases.
So the situation I've decribed (max_labels = 20, _increment = 175 and _max = 13900) becomes:

Безымянный1.png (72.19 KiB) Viewed 76702 times

My approach is not always perfect: when (Double)_max / _increment / _num is close to n.5 but slightly less there is same gap (but it is 2 times smaller). For example for _max = 12200 (12200/175/20 = 3.485, so _multiplier is still 3) I get the following picture:

Безымянный2.png (72.11 KiB) Viewed 76702 times

If you have any ideas how to further improve my adjusted algorithm - please share it. Thank you.

[Christopher]

If you have any ideas how to further improve my adjusted algorithm - please share it. Thank you.

How about:

Code: Select all

         private void TChart1_GetNextAxisLabel(object sender, GetNextAxisLabelEventArgs e)
        {
            var mod = _max % _increment;
            var local_max = _max;

            if(mod != 0) 
            {
                local_max = _max + (_increment - mod);
            }

            var max_labels = 20;
            var num = Utils.Round(local_max / _increment);
            var multiplier = Utils.Round(num / max_labels);

            int GetValue(int index)
            {
                return _increment * multiplier * index;
            }

            if (sender == tChart1.Axes.Left)
            {
                e.Stop = false;

                if(e.LabelIndex <= num)
                {
                    e.LabelValue = GetValue(e.LabelIndex);
                }
                else 
                {
                    e.Stop = true;
                }
            }
        }

[bairog]

Unfortunately with this code labels count can greatly exceed max_labels value. For example for _max = 5300 the are 30 labels:

Безымянный.png (69.46 KiB) Viewed 76693 times

[Christopher]

Unfortunately with this code labels count can greatly exceed max_labels value. For example for _max = 5300 the are 30 labels:

Yes, that's true. But I'm sure you get the idea now of what the TeeChart possibilities are, and so can adapt your code to them.