How to use TChart for simple Box-Whiskers plot?
lazarus / 55-TAChart

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stephanweber · 2019-06-17 13:23

Hi,

I have a chart and at the x-position x=1 I want to place a box-
whiskers element, e.g. with the 5 y-entries 0.50 ; 1.0; 1.5 ; 1.9; and
2.70.
How can I do this, e.g. using Addxy and an array yval[1..5] of double?
I need a simple code example, because currently I see only an empty
chart.

Bye Stephan

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wp · 2019-06-17 14:12

Just call the AddXY of the BoxAndWhiskerSeries which accepts all five
y values in the order lower whisker, lower box, center, upper box,
upper whisker:

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    
function AddXY(      AX, AYLoWhisker, AYLoBox, AY, AYHiBox,
AYHiWhisker: Double;      AXLabel: String = ''; AColor: TColor =
clTAColor): Integer; overload;
In your case:
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
Chart1BoxAndWhiskerSeries1.AddXY(1, 0.5, 1.0, 1.5, 1.9. 2.7);

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stephanweber · 2019-06-18 07:04

Thanks a lot!! Yesterday I experimented a lot and found this works:


    Chart1BoxAndWhiskerSeriesCpk.Clear;
    Chart1BoxAndWhiskerSeriesCpk.ListSource.YCount := 5;

    ylist[1]:=0.75;
    ylist[2]:=1;
    ylist[3]:=1.25;
    ylist[4]:=0.5;
    y0:=1.5;

    Chart1BoxAndWhiskerSeriesCpk.AddXY(1, y0, ylist);

So the order is really confusing, maybe a bug in my older Lazarus.

Bye Stephan

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wp · 2019-06-18 08:35

Read the documentation
https://wiki.lazarus.freepascal.org/TAChart_documentation#Multi-
valued_sources.

For TBoxAndWhiskerSeries, we need five y values. This means, in
addition to the ordinary y value, four y values will go into the
YList. BUT: YList is a zero-based array. This leads to some unusual
indexing:

*  "normal" y value --> y index 0 --> stored in Series.ListSource[i
]^.Y
*  first extra y value --> y index 1 --> stored in Series.ListSource[i
]^.YList[0]
*  second extra y value --> y index 2 --> stored in
Series.ListSource[i ]^.YList[1]
etc.

For 5 values in total, YList is allocated to get 4 values because the
other one is outside the array. This means, you have Y, YList[0],
YList[1], YList[2], YList[3]. There is not YList[4]! And you did not
assign anything to YList[0]...

I don't know whether this produces the effect that you mention.

But note: TBoxAndWhiskerSeries has an overloaded AddXY method where
you simply specify the y values in the order from lowest to highest -
this frees you from all these details.

The following code snippet compares both methods to add data to a Box-
and-whisker series:
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 procedure
TForm1.FormCreate(Sender: TObject);begin//
 Chart1BoxAndWhiskerSeries1.ListSource.YCount := 5; 
Chart1BoxAndWhiskerSeries1.AddXY(0, 0.5,  1.0, 1.5, 1.9, 2.7);   //
specialized for TBoxAndWhiskerSeries 
Chart1BoxAndWhiskerSeries1.AddXY(1, 0.5, [1.0, 1.5, 1.9, 2.7]);  //
valid for all series typesend;
Another note: If your Lazarus version is very old then you must
specify the YCount of the chart source before adding data:
BoxAndWhiskerSeries.ListSource.YCount := 5. In current versions, this
is no longer required.