Ploting Stock data with multiple days
lazarus / 55-TAChart

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chucky · 2013-04-22 06:41

I can produce a nice looking line series chart showing minute interval
stock price data but if a try to chart two days I get a large gap with
a long straight line between the days from 16:00 (market close) and
9:30 (market open) for the next day.

How can I eliminate this gap?

Here is how I set the chart:

  Chart := LzChart.Create(Self,Self,'MyChart',100,50,300,700); 
  LS := TLineSeries.Create(Chart);
  DT := TDateTimeIntervalChartSource.Create(Chart); 
  Chart.BottomAxis.Marks.Source := DT;
  Chart.BottomAxis.Marks.Style := smsLabel;

Then a for next loop to add the points for each day:

  LS.AddXY(MyDate,Close_Value);

Only data between 9:30 - 16:00 are added.

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wp · 2013-04-22 07:19

After each day add a NaN to the series (Series.AddNull; http://wiki.la
zarus.freepascal.org/TAChart_documentation#Skipping_source_items)

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chucky · 2013-04-24 01:30

I added a NaN data item between the days. It got rid of the straight
line but the large gap is still there.

The x axis needs to jump to 9:30 directly after the previous 16:00 and
ignore all the data points in between.

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wp · 2013-04-24 07:18

OK, I see what you mean. I hope your data are equiditant within each
day, otherwise it's more complicated.

In the equidistant case, simply plot against the data index: Don't use
AddXY to add the data to the series, use Add instead -- this uses the
index of the data point as x value; and add the date as data label
(i.e. Series.Add(value, FormatDateTime('hh:mm', datevalue)). In order
to show the axis labels you have to assign the ChartSource used for
the series to the BottomAxis of the chart (i.e:
Chart.BottomAxis.Marks.Source := Series.ListSource) and set the Style
of the BottomAxis marks to smsLabel.

As before, use AddNull to create the break. Probably (I did not test
what I am writing here) the gap will be 1 datapoint too wide because
the AddNull increases the point index. To avoid this, use a separate
variable for the data index and add the data by calling AddXY again,
but now using the dataindex explicity as the x value, i.e.
Series.AddXY(dataindex, value, FormatDateTime(...)). Increment
dataindex after each adding a data value, but don't increment it after
adding the null.