How to view the last 10 DataPoints in a chart that's updating each second?

Question

I have this code:

private void timer_Tick(object sender, EventArgs e)
    {
        timer.Stop();
        for (int i = 0; i < TOTAL_SENSORS; i++)
        {
            DateTime d = DateTime.Now;
            devices[i].Value = float.Parse(serialPort.ReadLine());
            if (chart1.Series[i].Points.Count > MAX_POINTS)
            {
                //see the most recent points
            }
            chart1.Series[i].Points.AddXY(d, devices[i].Value);
        }
        timer.Start();
    }

This part of my code is the timer's tick event where i draw a chart and i need to update it every tick.I keep adding points and when the points count reaches MAX_POINTS(10) it removes the first point and adds a new one at the end.

The problem is when it reaches MAX_POINTS it starts removing points at the end and the graph doesn't autoscroll. All points get deleted and no new points get added.

Please help me and say what I need to change the chart to work as I said.

EDIT 1: I am using Windows Forms.

EDIT 2: AddXY and RemoveAt are not mine they are from the points collection.

EDIT 3: I also want to know how to have a 'scope' and see the data for the last hour or for the last week or for the last month.

EDIT 4: I changed my question a bit, I now want to scale the chart to show the points from the last hour/day

Answer 1

Store the points in a separate dictionary as well as the chart. Then you can just query the dictionary when you want the most recent points.

Dictionary<DateTime, float> points = new Dictionary<DateTime, float>();

then add this line directly after your call to AddXY():

points.Add(d, devices[i].Value);

and if you want to keep the dictionary in sync with the chart, remove the first element from the dictionary as well:

points.Remove(points.Keys[0]);

---

To query the dictionary, you can use linq: Take() Documentation Skip() Documentation

IEnumerable<KeyValuePair<DateTime, float>> mostRecent = points.Skip(points.Count - 10).Take(10);

or you can get a specific point (lets say you want the point from one minute ago)

float value = points[DateTime.Now.AddMinutes(-1)];

or you can loop over the items:

foreach(KeyValuePair<DateTime, float> point in points)
{
    DateTime time = point.Key;
    float value = point.Value;
}