How to add a horizontal line to a bar chart?

Quick question that's been stumping me. I'm displaying some data in a stacked bar chart, where the total height of the stack should be compared to a target value. How can I draw a horizontal line on the chart to represent that target?

Thanks,
Chris

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bhanley

Hi,

This is pretty straightforward. On your stacked bar chart (or bar chart for that matter), go to the "Format Chart" tab of the wizard. Click on Y-Series (under the "Chart Area" on the left). Then click on the "Markers" button to add your marker.

I have attached a report design that does this. It uses the sample data base. A yellow line is added to the stacked bar chart.

Good Luck!

cjmaloof

Oh, awesome -- thanks!

I don't suppose there's any way to make the target depend on a report parameter? Even if not, it's still pretty helpful.

bhanley

I do not see a way to bind the target to a parameter. That does sound like a better way to do it though. 
 
I filed an enhancement request to have it looked at. You can track it here: 
 
<a class='bbc_url' href='http://ted.birt-exchange.com/show_bug.cgi?id=61'>Redirecting to BIRT Exchange</a>

cjmaloof

Bit of a bruising syntax-wrangling session, but I eventually met Rhino and pieced together enough documentation to come up with the following code for the onRender script of the chart: 
 
<pre class='_prettyXprint _lang-auto _linenums:0'>
importPackage(Packages.org.eclipse.birt.chart.model.data.impl);
function beforeDrawMarkerLine( axis, markerLine, icsc ) {
target = icsc.getExternalContext().getScriptable().getParameterValue("total_target");
markerLine.setValue(NumberDataElementImpl.create(target));
}</pre>
 
which changes the line position at runtime.

bhanley

Very cool. Thanks for sharing the code.

Susmitha

Hi,
is "total_target" in the script is a global variable? I am getting error when I pass dataset variable in the getParameterValue () method. Can you please let me know how can I declare/pass backend table column to the getParameterValue method.

Thanks,
Susmitha.

cjmaloof

total_target is a report parameter. Since icsc.getExternalContext().getScriptable() returns an IReportContext ( see <a class='bbc_url' href='http://www.birt-exchange.org/documentation/BIRT_220/EngineJavadoc/enginescript/api/index.html'>Birt Script API</a>) you could use getGlobalVariable() to get a global variable. 
 
I'm not sure about computing a marker line from the dataset -- don't know if the data series values are available when the line is drawn. If they are, I guess you could use the afterDataSetFilled event to compute a value and store it in a global variable for use by beforeDrawMarkerLine?

oespinosa

Hi.

I add two lines marks giving them value parameters as it ago?

TTman

how to fix the marker (Target Line). I have added two lines to define min and max values on y-axis. But they are not fixed, they are moving constantly as data changes. Thanks in advance.

jfranken

To create a fixed line at y=10, add code like the following in the chart's beforeGeneration method:

fixedLine = MarkerLineImpl.create(yAxis, NumberDataElementImpl.create(10));