How to Build an ExtJS 3.4 Scatter Chart with Logarithmic Axis

Problem

You're rendering data that increases exponentially, and wish to display a chart with a log-scale axis.

Exponential data:

Logarithmic scale rendering of the same:

Solution

Set the “scale” property of the relevant axis to “logarithmic.”

Discussion

There does not seem to be any way to control the frequency of the major/minor tick marks other than by fixed intervals. Be careful about setting these in this chart type, as you can quickly overwhelm the browser to the point where Flash is unresponsive. It may be preferable to control the rendering using tooltips on the data points.

For further discussion of similar charts, see the ExtJS scatter chartexample and ExtJS trend line example.

Ext.onReady(function() {
Ext.chart.Chart.CHART_URL = 'ext-3.4.0/resources/charts.swf';
   var store = new Ext.data.JsonStore({
    fields: ['year', 'action'],
    data: [
        {year: 2005, action: 100000},
        {year: 2006, action: 1000000},
        {year: 2007, action: 10000000},
        {year: 2008, action: 100000000}
        ]
  });
 
  new Ext.Panel({
    width: 390,
    height: 300,
    renderTo: 'container',
    title: 'Scatter Plot - Takings by Genre',
    items: {
      xtype: 'linechart',
      store: store,
      xField: 'year',
      xAxis: new Ext.chart.NumericAxis({
        minimum: 2004,
        maximum: 2009,
        majorUnit: 1,
 
      }),
      yAxis: new Ext.chart.NumericAxis({
        labelRenderer: Ext.util.Format.usMoney,
        minimum: 10,
        maximum: 1000000000,
        scale: 'logarithmic'
      }),
      series: [{
        yField: 'action',
        displayName: 'Action',
        style: {
          lineAlpha: 0.0
        }
      }]
    }
  });
});