Question about TBarSeries
lazarus / 55-TAChart

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ProgEd · 2013-03-15 00:22

I'm generating a graph as the result of some calculations. So far I've
got the bar chart rotated so I have horizontal bars. Now I want to
specify a max value for the Y axis (a range of 0 to 100). I'm also
coding the instruction to add data as follows:

FBar.AddXY(I, R, sCategories, clRed)

where I is the X value (runs from 1 to 17) and R is the Y value
(between 0 and 100). I'm assuming from the documentation that the
third field would be the label that would be placed on the data, but I
only get numbers, not the text. Clearly I have missed something, but
what?

So, the two questions: how do I specify a range for an axis and how do
I get text on the axis?

Thanks,

Ed

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fred1933 · 2013-03-15 07:38

Hi,
if you use TChart component, you can specify a range for X or/and Y
axis by changing extent.XMax, extent.YMax.. extent.UseXMax,... fields
of TChart component. You can directly change parameters in objects
inspector.

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wp · 2013-03-15 08:33

You question regarding the axis labels is answered in http://www.lazar
us.freepascal.org/index.php/topic,19820.msg113355.html#msg113355

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ProgEd · 2013-03-15 15:22

Thanks for the two answers, they have helped. But I still have a small
(major?) problem. The graph is drawn exactly the way I want it, but
the labels on the axis are very inconsistent. Here's the code I'm
using:

Code: [Select]procedure TForm1.DoChart(Sender: TObject);
var
   I:                               Integer;
begin
   If FBar = nil then
      begin
         FBar := TBarSeries.Create(Chart1);
         FBar.AxisIndexX := 0;        { Rotate the }
         FBar.AxisIndexY := 1;        { graph axis }
         Chart1.AddSeries(FBar);
         FBar.Source := CSource;
         Chart1.Extent.UseXMax := True;
         Chart1.Extent.UseXMin := True;
         Chart1.Extent.XMax := 100;
         Chart1.Extent.XMin := 0;
         Chart1.LeftAxis.Marks.Source := CSource;
      end;
   For I := 1 to 19 do
      Begin
         If iPct[I] < 70 then
            CSource.Add(I, iPct[I], sCategories[I], clRed)
         Else
            CSource.Add(I, iPct[I]; sCategories[I], clBlue);
      end;
end;
I can see the text being added to the CSource, but only some of the
text values actually show up on the chart. Any ideas?

Ed

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wp · 2013-03-15 21:46

What is "inconsistent"? Could you post a screenshot to explain what
the issue is?

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ProgEd · 2013-03-16 01:16

I've been trying to send it, but the server keeps rejecting saying
it's taking too long or is too big. Here's what I'm seeing, however,

The chart formats the data correctly. The titles for each bar should
be down the left side for each of the 19 bars. Only some are showing
-- and that number varies! They are also shown out of order. For
example, with one set of data I might see this:

A   xxxxxxxxxxxxx
     xxxxxxx
     xxxxxxxxxxxxxxxxxxxx
C   xxxxxxxxxxxxxxxxxx

And with a different set of data, totally different text will be shown
or omitted.

Ed

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wp · 2013-03-16 12:00

Ok, I tried a demo on my own and could verify the issue. I guess,
however, that this is not a bug, but a feature. You have to understand
how the axis marks work: when you populate a listsource the first two
parameters of the Add command are understood as the x and y
coordinates, respectively, to which the label text is assigned. So, if
you want the labels to appear at the y axis their coordinate is taken
from the second parameter. But you had rotated the series which means
that the y axis gets the values of the x axis, but the chart source
finds the label positions from the original y values assigned to the
chart source.

A solution is to use a second list source for the labels alone. If you
don't want to label the bars, you can drop the texts from the original
source to save memory. The following idea works in my demo:

Code: [Select]var
  CDataSource: TListChartSource;
  CLabelSource: TListChartSource;
begin
   for I := 1 to 19 do begin
      If iPct[I] < 70 then
        CDataSource.Add(I, iPct[I], '', clRed)
      else
        CDataSource.Add(I, iPct[I]. '', clBlue);
      CLabelSource.Add(I, I, sCategories[I]);
  end;
end;

The CDataSource is to be assigned to the Source property of the
BarSeries, and the CLabelSource goes to the Source of yAxis.Marks.

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ProgEd · 2013-03-16 13:17

Thanks, that resolved the issue. I do, however, think it's a bug.
Clearly the chart knows it's rotated, so one would think that the
labels should also rotate. But the work-around you suggested has given
me what I wanted.

I really appreciate the help.

Ed

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wp · 2013-03-16 21:18

QuoteClearly the chart knows it's rotated, so one would think that the
labels should also rotate. This is only true for this simple chart. In
general there are several series assigned to the axes, and they can be
rotated or not. I know that this is not very common, but TAChart is
flexible enough to handle even this case. Therefore it is a "feature",
not a bug.