Friday, July 2, 2021



Last week I was playing around with some data and could not find the right chart to visualize it.

To give you an idea about the data, let's take the harvest of some fruits as an example. You will have ripe and unripe fruits, fruits that have been eaten by birds or caterpillars. Some of them might have been damaged by hail or did not get enough water, others might be rotten or mouldy. For each fruit you have those different numbers and you have the sum of each fruit and the sum of all fruits.

The best way to compare all those numbers would be a matrix style chart. So I've stumbled upon the so called Bubble Grid Chart. So here is an example that I've found on the web:

As you can see it shows the fruit data that I described above.

The value of each crosspoint e.g. 90 Apples that are ripe will be visualized by the size of the bubble. Sizing the bubbles is a bit tricky because you would like to avoid having a few big bubbles and a lot of tiny bubbles. So you need to make sure that the size of the bubbles has no linear relationship to it's value.

In addition the max size of a bubble is given by either the height of the y-category items or the width of the x-category items, depends on which is smaller.

I also would like to have a grid in the background to make it easier to find specific coordinates. So, long story short, here is my version of the BubbleGridChart:

As you can see I've decided to put the x-category items on the bottom and also added the ability to show not only the values on the bubbles but also on the rows and columns of the chart. I really was impressed on how much information you can get out of one chart. At a glance you can see that the number of all ripe fruits is 215 which is 43% of all fruits. Because in this example the number of each fruit was always 100 you cannot really compare by the x-category but this could be different.

You can see that 90 Apples have been ripe which is 18% of all fruits. This information will be shown in a little info that will popup when you click on the bubble. In addition I've added the ability to sort the chart in x- and y-direction by either their indices or their values.

To be able to sort the items by their index you have to define it upfront.

Let me show you how to set up the x- and y-category items for the chart above.

Y-Category Items:

ChartItem ripe = ChartItemBuilder.create().name("Ripe").index(0).fill(Color.BLUE).build();

ChartItem unripe = ChartItemBuilder.create().name("Unripe").index(0).fill(Color.RED).build();

X-Category Items:

ChartItem peaches = ChartItemBuilder.create().name("Peaches").index(0).fill(Color.ORANGERED).build();

ChartItem apples = ChartItemBuilder.create().name("Apples").index(1).fill(Color.LIMEGREEN).build();

BubbleChart Items:

BubbleGridChartItem peaches1 = BubbleGridChartBuilder.create().categoryXItem(peaches).categoryYItem(ripe).value(60).fill(Color.ORANGERED).build();

BubbleGridChartItem peaches2 = BubbleGridChartBuilder.create().categoryXItem(peaches).categoryYItem(unripe).value(5).fill(Color.ORANGERED).build();

BubbleGridChartItem apples1 = BubbleGridChartBuilder.create().categoryXItem(apples).categoryYItem(ripe).value(90).fill(Color.LIMEGREEN).build();

BubbleGridChartItem apples2 = BubbleGridChartBuilder.create().categoryXItem(apples).categoryYItem(ripe).value(0).fill(Color.LIMEGREEN).build();

The index that you define will later be used to sort the items, just make sure you don't have duplicate indices because I do not check that at the moment (I just needed something that works quickly). So you first create the x- and y-category items and from those you create the actual BubbleGridChart items that will be used to visualize the chart.

The BubbleGridChart itself can be create as follows:

BubbleGridChart bubbleGridChart = 
                          .gridColor(Color.rgb(255, 255, 255, 0.1))
                          .gradient(new LinearGradient(0, 0, 1, 0, true
                                    new Stop(0, Color.BLUE), 
                                    new Stop(1, Color.RED))

Sorting the categories via the build only works if you also provide the items, otherwise you have to call the sorting methods like sortXCategoryItemsByIndexAscending() after you have added the bubbleGridChartItems. For me the charts now works fine but you might have other requirements, so please do not hesitate to file issues/request over at github.

The BubbleGridChart can be find in the current jdk16 branch which is also available on maven central. The jdk16 branch is more a temporary branch that I use to test stuff before JDK17 will come out in September. Because this will be the next long term stable version I will create a jdk17 branch in the future which will become the new main branch then.

That's it for today, so enjoy the upcoming weekend and...keep coding... :)

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