Assuming your data are plotted as a scattergraph using the ChartType.Points
the simplest way to add a line is to add one extra Series
with ChartType.Line
and set two points there.
There are other ways to create a line on a Chart
, like drawing it or creating a LineAnnotation
, but they are much more complicated!
Following this example to the letter here is an implementation:
Note that after creating the series for the line of best fit the thing you were looking for are just the last two lines..:
private void button1_Click(object sender, EventArgs e)
{
// create TWO series!
chart1.Series.Clear();
chart1.Series.Add("Data");
chart1.Series.Add("Line of best fit");
chart1.Series[0].ChartType = SeriesChartType.Point;
chart1.Series[1].ChartType = SeriesChartType.Line;
List<int> levels = new List<int>() { 8, 2, 11, 6, 5, 4, 12, 9, 6, 1};
List<int> scores = new List<int>() { 3, 10, 3, 6, 8, 12, 1, 4, 9, 14};
double minX = levels.ToList().Min();
double maxX = levels.ToList().Max();
double meanX = 1f * levels.Sum() / levels.Count;
double meanY = 1f * scores.Sum() / scores.Count;
double st = 0;
double sb = 0;
for (int i = 0; i < levels.Count; i++ )
{
st += (levels[i] - meanX) * (scores[i] - meanY);
sb += (levels[i] - meanX) * (levels[i] - meanX);
}
double slope = st / sb;
double y0 = meanY - slope * meanX; // y-intercept or y-crossing
for (int i = 0; i < levels.Count; i++)
{
chart1.Series[0].Points.AddXY(levels[i], scores[i]);
}
// this is the part that creates the line of best fit:
chart1.Series[1].Points.AddXY(minX, y0 + minX * slope);
chart1.Series[1].Points.AddXY(maxX, y0 + maxX * slope);
}
If you want to you can add the first line point right at the y-axis:
chart1.Series[1].Points.AddXY(0, y0 );
In this case you may want to set the minimum x-values shown in the chart to prevent it from including -1
, maybe like this:
chart1.ChartAreas[0].AxisX.Minimum = minX - 1;
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