Question

I’m using Flex for charting time series data. the data range is from 2002 to 2009, however the data is not available for some periods of time (i.e from 4/2004 to 8/2005). The following lines show the tags I’m using for the chart:

<mx:Canvas id="cp" backgroundColor="#ffffff" fontFamily="Verdana" fontSize="12" color="#093A89" fontWeight="bold" width="100%" height="100%" alpha="1" creationComplete="init()">
<mx:LineChart id="cChart"  showDataTips="true" paddingRight="40" paddingLeft="30" width="100%" height="85%">
    <mx:verticalAxis>
        <mx:LinearAxis id="linearAxis" baseAtZero="false" title="{parameterLabel}" minorInterval="0.5" interval="1.0"/>
    </mx:verticalAxis>
    <mx:verticalAxisRenderers>
        <mx:AxisRenderer axis="{linearAxis}" fontSize="10">
            <mx:axisStroke>
                <mx:SolidColorStroke weight="6" color="#BBCCDD" alpha="1" caps="square"/>
            </mx:axisStroke>                    
        </mx:AxisRenderer>
    </mx:verticalAxisRenderers>
    <mx:horizontalAxis>
        <mx:DateTimeAxis id="ca" minimum="{sDate}" maximum="{eDate}" title="Date" dataUnits="days" dataInterval="1" labelUnits="days"/> 
    </mx:horizontalAxis>
    <mx:horizontalAxisRenderers>
        <mx:AxisRenderer axis="{ca}" canDropLabels="true" fontSize="10" labelRotation="45">         
            <mx:axisStroke>
                <mx:SolidColorStroke weight="6" color="#BBCCDD" alpha="1" caps="square"/>
            </mx:axisStroke>                    
        </mx:AxisRenderer>              
    </mx:horizontalAxisRenderers>
    <mx:series>
        <mx:LineSeries id="l1" visible="false"/>
    </mx:series>
</mx:LineChart>
<mx:Legend id="mylgn" horizontalCenter="0" bottom="32"/>
<s:Label id="lblChart1" text="{dataType} {parameterLabel} at {streamLabel}" horizontalCenter="0" bottom="20"/>
<s:Label id="lblChart2" text="{optionalText}" horizontalCenter="0" bottom="5"/>

The following image illustrates the chart created by the above code:

As you can see there are gaps for the intervals with no data. Is there any way to remove/cut the intervals with no data? What is the best practice for this type of data?

Any thoughts or recommendation would be much appreciated

Answer 1

This is accomplished via an adapter to your dataProvider.

To show a horizontal line between missing samples, you must add an additional sample to your data provider with value equal to the last sample.

If you had time series data of:

timestamp    value
4/2004       3
8/2005       23

You would add an additional sample immediately before 8/2005 equal to the previous value of 3.

timestamp    value
4/2004       3
7/2005       3 <-- insert sample
8/2005       23

Instead of interpolating between values 3 and 23, a flat horizontal line is displayed.

Sample data model

package
{
    public class TrendData
    {
        public var timestamp:Date;
        public var value:Number;
    }
}

Static adapter utility

package
{
    import mx.collections.ArrayList;

    public class TimeSeriesDataAdapter
    {

        public static function interpolate(data:ArrayList):ArrayList
        {
            var set:ArrayList = new ArrayList();
            var timespan:Number;

            // add first sample:
            set.addItem(data[0]);

            for (var i:uint = 1; i < data.length; i++)
            {
                // measure timestamp between current sample and last sample
                timespan = TrendData(data[i]).timestamp.time - TrendData(data[i-1]).timestamp.time;

                // if the timespan is greater than desired range (1-day), add a sample
                if(timespan >= 86400000)
                {
                    var trendData:TrendData = new TrendData();

                    // set timestamp just before sample
                    trendData.timestamp = new Date(TrendData(data[i]).timestamp.time - 1);

                    // set value to previous value
                    trendData.value = TrendData(data[i-1]).value;

                    set.addItem(trendData);
                }

                set.addItem(data[i]);
            }

            return set;
        }

    }
}

Data Visualization implementation

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
               xmlns:s="library://ns.adobe.com/flex/spark"
               xmlns:mx="library://ns.adobe.com/flex/mx">

    <fx:Script>
        <![CDATA[
            import mx.collections.ArrayList;

            [Bindable]
            [ArrayElementType("TrendData")]
            public var data:ArrayList
        ]]>
    </fx:Script>

    <mx:LineChart dataProvider="{TimeSeriesDataAdapter.interpolate(data)}" />

</s:Application>