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I am making a chart that displays network latency and connection failure rate on graph. I am using DefaultCategoryDataset to store the data, but the problem is, that this dataset uses String for the X axis values:

  DefaultCategoryDataset dataset = new DefaultCategoryDataset( );
  dataset.addValue( 15 , "Line name" , "X value" );

Since I render packets based on Unix time in miliseconds, it ends up looking like this:

image description

I'd like to fix it so that:

  1. New values (larger timestamp) appear to the right, not left
  2. X labels too close to each other are inteligently merged, as on this image: image description

To generate the dataset, I run over array of samples and end up with two HashMap<String, Double> representing average latency and failure rate. These are then assigned as follows:

//Latency line
for (Map.Entry<String, Double> entry : time.entrySet())
{
  dataset.addValue(entry.getValue(), "Average ping [ms]", entry.getKey());
}
//Fail rate line
for (Map.Entry<String, Double> entry : fail_rate.entrySet())
{
  dataset.addValue(entry.getValue()*100, "Fail rate [%]", entry.getKey());
}
Tomáš Zato
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    Does the chart require Categories? Don't get the full scope of the data, but it seems an `XYDataset` would suffice. AFAIK The CategoryAxis will attempt to draw all labels without discrimination. Other charts - such as a NumberAxis or DateAxis are more reserved when rendering the labels. – copeg May 26 '15 at 20:07
  • @copeg Thank you, I'll google the things you mentioned. I used the category axis because that's what they used in some online tutorial... – Tomáš Zato May 26 '15 at 20:11

2 Answers2

2

For this type of graph I think you should use a XYDataset with TimeSeriesand DateAxis. There is one example demonstrated here: http://www.jfree.org/jfreechart/api/javadoc/src-html/org/jfree/chart/demo/TimeSeriesChartDemo1.html

You can also use a custom Timeline implementation for your DateAxis, in particular to control the orientation of the dates (more recent to the right). More information here: http://www.jfree.org/jfreechart/api/javadoc/org/jfree/chart/axis/Timeline.html

Eric Leibenguth
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2

If your data does not require the use of Categories, you can use an XYDataset, and create an XY plot eg using ChartFactory.createXYLineChart. 

DefaultXYDataset ds = new DefaultXYDataset();
//generate random data as an example
double[][] data = new double[2][1000];
for ( int i = 0; i < 1000; i++ ){
    data[0][i] = i;
    data[1][i] = (Math.random() * 100);
}
ds.addSeries("Time", data);
JFreeChart chart = ChartFactory.createXYLineChart("Test", "Time", "Y-Axis", ds, PlotOrientation.VERTICAL, false,false,false);

In this manner, problem (2) should take care of itself (and you could make use of the DateAxis class for rendering the time). For problem (1), using this type of axis you can just invert it:

myChart.getXYPlot().getRangeAxis().setInverted(true);
copeg
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