generate a trendline from files in a chart

I want to be able to fetch .csv files from a folder and plot them up in a chart.

Currently, I'm just saving the files and displaying an individual curve like this:

RunTest function:

public List<Tuple<double,double>> runTest()
{
    _dpg = new Root(this, "english", false);
    _dpg.Init();
    var filename = "Dpg10Export_" + DateTime.Now.ToString("yyyyMMdd_HHmm") + ".csv";
    List<Tuple<double, double>> results = new List<Tuple<double, double>>();

    var measurement = new Measurement();
    var resultCode = RunMeasurement(60, 1000, 2200, ref measurement, null /* TODO: ref ProgressBar? */);

    using (var fileStream = new StreamWriter(filename))
    {
        var count = measurement.I_inc_Values.Count;

        for (var i = 0; i < count; i++)
        {
            var item = measurement.I_inc_Values[i + 1];
            var current = (float)Convert.ToDouble(item);

            item = measurement.LI_inc_Values[i + 1];
            var inductance = (float)Convert.ToDouble(item);

            var line = current.ToString() + ";" + inductance.ToString() + ";";

            fileStream.WriteLine(line); 
            currentList.Add(current);
            inductanceList.Add(inductance);
            results.Add(new Tuple<double, double>(current,inductance));
            if (i == 0 || (i + 1) % 32 == 0)
            {
                Console.WriteLine((i + 1) + ": " + line);
            }
        }
    }
    return results;
}

This code produces a csv-file that looks something like this:

0,22 | 0,44

0,32 | 0,54

0,44 | 0,65

And those values produce a curve that looks like this:

When you click on the "get Waveform" button, the curve above is generated. However, I want to display all the curves that has been generated, and a trendline as well. How would I achieve this?

void BindData(List<Tuple<double,double>> results)
{
    chart.Series.Clear();
    var series1 = new System.Windows.Forms.DataVisualization.Charting.Series
    {
        Name = "curr/induc",
        Color = System.Drawing.Color.Green,
        IsVisibleInLegend = true,
        IsXValueIndexed = true,
        ChartType = SeriesChartType.Line                
    };

    foreach (var i in results)
    {
        series1.Points.AddXY(i.Item2,i.Item1);
    }

    chart.Invalidate();
    chart.Series.Add(series1);
}

private void getWaveformBtn_Click(object sender, EventArgs e)
{
    Dpg10Client.Dpg10Settings settings  = new Dpg10Client.Dpg10Settings();
    Dpg10Instrument hej                 = new Dpg10Instrument(settings);
    List<Tuple<double,double>> results  = hej.runTest();
    double current, inductance;

    foreach(var i in results)
    {
        current = i.Item1;
        inductance = i.Item2;
        textBoxWaveformInput.Text += current.ToString() + inductance.ToString();
    }
    BindData(results);         
}

TL;DR

Parse the information from the CSV files to generate curves, and create a trendline based on those files.

Marked as duplicate: That answer is regarding a straight line, these values can fluctuate in a curve.

There are many ways to solve most of the various problems in your question.

Let me tackle only the one that actually has to do with calculating an average from multiple series, i.e. will not deal with creating a Series with data from a CSV file.

There is a built-in class that can do all sorts of advanced math, both financial and statistical, but I didn't find one that will help in creating an average line/curve over more than one series.

So let's do it ourselves..

The first issue is that to calculate averages we need not just data but the data, that is their x-values, must be grouped into 'bins' from which we want to get the averages.

Unless the data already are grouped like that, e.g. because they have one value per series per day, we need to create such groups.

Let's first collect all the points from all series we want to handle; you may need to adapt the loop to include just your set of series..:

var allPoints = new List <DataPoint>();
for (int s = 0; s < 3; s++)  // I know I have created these three series
{
    Series ser = chartGraphic.Series["S" + (s+1)];
    allPoints.AddRange(ser.Points);
}

Next we need to decide on a bin range/size, that is a value that determines which x-values shall fall into the same bin/group. I chose to have 10 bins.

So we best get the total range of the x-values and divide by the number of bins we want..:

double xmax = allPoints.Max(x => x.XValue);
double xmin = allPoints.Min(x => x.XValue);
int bins = 10;
double groupSize = (xmax - xmin) / (bins - 1);

Next we do the actual math; for this we order our points, group them and select the average for each grouped set..:

var grouped = allPoints
                .OrderBy(x => x.XValue)
                .GroupBy(x => groupSize * (int)(x.XValue /groupSize ))
                .Select(x => new { xval = x.Key, yavg = x.Average(y => y.YValues[0]) })
                .ToList();

Now we can add them to a new series to display the averages in the bins:

 foreach (var kv in grouped) avgSeries.Points.AddXY(kv.xval + groupSize/2f, kv.yavg);

I center the average point in the bins.

Here is an example:

A few notes on the example:

The average line doesn't show a real 'trend' because my data are pretty much random.

I have added Markers to all series to make the DataPoints stand out from the lines. Here it is how I did it for the averages series:

avgSeries.MarkerStyle = MarkerStyle.Cross;
avgSeries.MarkerSize = 7;
avgSeries.BorderWidth = 2;

I have added a StripLine to show the bins. Here is how:

StripLine sl = new StripLine();
sl.BackColor = Color.FromArgb(44,155,155,222);
sl.StripWidth = groupSize;
sl.Interval = groupSize * 2;
sl.IntervalOffset = chartGraphic.ChartAreas[0].AxisX.IntervalOffset;
chartGraphic.ChartAreas[0].AxisX.StripLines.Add(sl);

I have also set one point to have a really low value of -300 to demonstrate how this will pull down the average in its bin. To keep the chart still nicely centered on the normal range of data I have added a ScaleBreakStyle to the y-axis:

chartGraphic.ChartAreas[0].AxisY.ScaleBreakStyle.BreakLineStyle = BreakLineStyle.Wave;
chartGraphic.ChartAreas[0].AxisY.ScaleBreakStyle.Enabled = true;