[SOLVED] Charts: how to add a new point and erase the oldest one?
lazarus / 61-Beginners

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valford · 2018-01-25 05:46

Hello,
(I'm going to say sorry about my English in advance xD).
I am creating a chart with data which came every one second (one point
per second). I can create the chart but after an hour is full of point
and is difficult to see the detail of the last point o the last few
points. I do not want to do a zoom manually, I want to have a maximum
number of points in my chart (we will say 60 points) and after that
delete one point from the beginning and add the new one in the line
("moving" the X axis, I do not want to restart the point number). So
when the point number 61 will add I should erase the point number 1;
add 62, erase 2; 63-3... and so on.

I have been trying to do it using the object inspector and the
AxisTransformation, but now I am running off of ideas 

Does someone know how to do it?

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wp · 2018-01-25 08:39

I assume that you add datapoints to the series by calling one its Add*
methods, i.e. Series.AddXY(x, y). Then the data are stored in a
TChartListSource which is accessible as Series.ListSource. Every
ChartListSource has a property Count telling you the number of data
points stored, and a method Delete(AIndex) which delete the datapoint
with the specified index. Therefore, you just delete the 0-th data
point if the Count is larger than the allowed value:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i if
Series.ListSource.Count > MAX_POINTS_VISIBLE then 
Series.ListSource.Delete(0);
Since in case of a LineSeries (or other descendants of
TBasicPointSeries) some properties of the ListSource are passed to
properties of the series you can also write
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i if
Series.Count > MAX_POINTS_VISIBLE then  Series.Delete(0);
The attached demo works this way. In addition it also sets the
LogicalExtent of the chart in order to obtain a smoother display. Note
that the code assumes that the x values are equal to the point index;
otherwise modifications are required, but I hope you get the idea

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valford · 2018-01-29 05:13

Thanks, it works perfectly!