Creating a simple stacked column chart – Flex

When I was working with Flex and Action Script 3.0 I used to do a lot of Dashboard and data visualization applications. One thing that I used to do often was a stacked column chart displaying multi dimensional data. So I thought of posting an example of creating a stacked chart out of the files deep within my Flex project folders. Let’s see the demo first and then move on to the explanation.

Demo: http://jbk404.site50.net/flex/playvideo/stackedchart.html

Stacked Column Chart
Stacked Column Chart - data visualization for three countries

Why a stacked chart?
In a normal column chart we show two dimensional data for the item that we are charting. One axis shows the category of division and the other shows the value. If you see the demo app or the picture above the x-axis categorizes the data into months and the y-axis shows the values. The item that we are charting is countries (India, USA, and Brazil). Had it been a normal column chart then we would have only one country data to visualize. That single country would have been our charting item (the object for which we are plotting the data). But in this case we have three countries and their data to visualize. So to do it all in a single chart we need a stacked chart in which one column (one particular month) is a stack of the values (individual columns) of each of the three counties. Below is the data structure that we will plot in the stacked column chart,

private var stackedData:ArrayCollection = new ArrayCollection([
{month:"Jan 2009",unitedstates: 200, india:101, brazil: 25},
{month:"Feb 2009",unitedstates: 100, india:34, brazil: 2},
{month:"March 2009",unitedstates: 50, india:10, brazil: 35},
{month:"Sep 2009",unitedstates: 160, india:51, brazil: 25},
{month:"Oct 2009",unitedstates: 20, india:20, brazil: 100},
]);

I will not go into the explanation of each of the classes (such as ArrayCollection) that I am using here, as this example is meant for someone who is familiar with Flex and ActionScript.
Had we been plotting a normal column chart the data structure would have been something like it is below,

private var data_normal_column_chart:ArrayCollection = new ArrayCollection([
{month:"Jan 2009",india:101},
{month:"Feb 2009",india:34},
{month:"March 2009,india:10},
{month:"Sep 2009",india:51},
{month:"Oct 2009",india:20},
]);

Writing the MXML code – creating the chart component

<mx:VBox width="100%" height="100%">
  <mx:ColumnChart id="chart" width="500" height="500" dataProvider="{stackedData}" showDataTips="true">
    <mx:horizontalAxis>
      <mx:CategoryAxis categoryField="month"/>
    </mx:horizontalAxis>
    <mx:series>
      <mx:ColumnSet type="stacked">
        <mx:ColumnSeries yField="unitedstates" displayName="United States"/>
        <mx:ColumnSeries yField="india" displayName="India"/>
        <mx:ColumnSeries yField="brazil" displayName="Brazil"/>
      </mx:ColumnSet>
    </mx:series>
  </mx:ColumnChart>
  <mx:Legend dataProvider="{chart}" direction="horizontal"/>
</mx:VBox>

To create a stacked chart we have to use the ColumnChart component. You can use the ColumnChart to represent a variety of different charts including simple columns, clustered columns, stacked, 100% stacked, and high/low. To visualize the data in our data structure (stackedData) it is data binded to the chart using the dataProvider property. And then we have set the showDataTips property to true so that a tooltip displays the necessary information for each column when user moves his mouse over it. The horizontal or the x-axis is a category axis which categorizes the data by months and I have specified the categoryField to month which is defined in the data. You use the ColumnSeries chart series with the ColumnChart control to define the data for the chart. A ColumnChart control expects its series property to contain an array of ColumnSeries objects. Now, to stack the columns use the ColumnSet grouping and set the type property to stacked. There are other options available for type property to define the grouping behavior of the chart series – clustered, 100%, overlaid. You can check them out in the ColumnSet link that I have given. You can see in the code that for each ColumnSeries I have specified the data for the country that it will display in the yField property. The displayName displays the value in the tooltip and the legend. This is all to create a simple stacked column chart. And finally we have the legend component that shows the chart legend.
Below is the full source code. You can copy the code and paste it in an .mxml file inside any of your project.

<?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"
width="100%" height="100%"
pageTitle="Stacked Column Chart">
<fx:Script>
<![CDATA[
import mx.collections.ArrayCollection;

[Bindable]
private var stackedData:ArrayCollection = new ArrayCollection([
{month:"Jan 2009",unitedstates: 200, india:101, brazil: 25},
{month:"Feb 2009",unitedstates: 100, india:34, brazil: 2},
{month:"March 2009",unitedstates: 50, india:10, brazil: 35},
{month:"Sep 2009",unitedstates: 160, india:51, brazil: 25},
{month:"Oct 2009",unitedstates: 20, india:20, brazil: 100},
]);

]]>
</fx:Script>

<mx:VBox width="100%" height="100%">
  <mx:ColumnChart id="chart" width="500" height="500" dataProvider="{stackedData}" showDataTips="true">
  <mx:horizontalAxis>
    <mx:CategoryAxis categoryField="month"/>
  </mx:horizontalAxis>
  <mx:series>
    <mx:ColumnSet type="stacked">
      <mx:ColumnSeries yField="unitedstates" displayName="United States"/>
      <mx:ColumnSeries yField="india" displayName="India"/>
      <mx:ColumnSeries yField="brazil" displayName="Brazil"/>
    </mx:ColumnSet>
  </mx:series>
  </mx:ColumnChart>
  <mx:Legend dataProvider="{chart}" direction="horizontal"/>
</mx:VBox>
</s:Application>

Here is the link to the demo once again: http://jbk404.site50.net/flex/playvideo/stackedchart.html

You can find a detailed tutorial on creating stacked chart- by Adobe in this link: http://help.adobe.com/en_US/flex/using/WS2db454920e96a9e51e63e3d11c0bf69084-7c6b.html

8 thoughts on “Creating a simple stacked column chart – Flex

  1. I’m impressed, I must say. Really rarely do I encounter a blog that’s both educative and entertaining, and let me tell you, you have hit the nail on the head. Your idea is outstanding; the issue is something that not enough people are speaking intelligently about. I am very happy that I stumbled across this in my search for something relating to this.

  2. In stacked column chart if the last array i.e month:”Oct 2009″,unitedstates: 20, india:20, brazil: 100 does not contain unitedstates then the last column in chart displays the value as 0. Ideally it shoud not display unitedstates.
    Please provide me the solution for this.

  3. Thanks for a marvelous posting! I genuinely enjoyed reading it,
    you might be a great author.I will be sure to bookmark
    your blog and will often come back later on. I want to encourage you to continue your
    great work, have a nice morning!

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