Used only in polar coordinates, the sector element is usually for plotting a pie chart. Here we’ll explain how it is employed and its properties.
1. Data properties
Through the following pie chart for displaying vault results, we’ll discuss the basics of plotting the sector element.
|2||=demo.query(“select * from GYMSCORE where Event = ‘Vault'”)|
A1 creates a canvas. A2 retrieves plotting data:
A3 plots the background. A4 plots an enumeration axis as the polar axis x. A5 plots a numeric axis as the radial axis y. The Allow Labels property of both axes is set specifically as false, so that tick marks will not be plotted on the polar axis in case of causing confusion to the pie chart plotting.
A6 plots the pie chart using the sector element, which is our focus in this article.
First look at the plotting result of A7:
When plotting a pie chart with the sector element, we plot a sector based on each group of data. A sector is a circle with its inside diameter being zero. The radial axis is a numeric axis showing scores of the athletes, according to which sectors are plotted successively with different central angels to eventually form a circle. A pie chart is in this sense similar to a stacked column chart discussed in esProc Charts: The Column Element. Like a column, one sector can be positioned by only one data point whose angular value will be calculated cumulatively. A6 specifies the data properties of the sector element:
Here the given logical coordinates A2.(NAME) and A2.(SCORE) on both axes are sequences. Different from plotting a column chart, the plotting of a pie chart with single data series will identify the enumeration value on the enumeration axis, i.e. the polar axis, always as 1, which means only one pie will be plotted.
2. Appearance properties
As can be seen from the chart above, the result of plotting with the sector element is sectors with fill colors. This means the appearance properties of the sector element will include fill color, border style, border weight and border color. By default, the fill color is automatically generated with lighting effects. Now modify A6’s code into =A1.plot(“Sector”,”borderWeight”:1,”borderColor”:-16724839,”fillColor”:[[“ChartColor”,0,true,-52429,-13057,0],[“ChartColor”,0,true,-10066177,-3355393,0],[“ChartColor”,0,true,-13369345,-1,0]],”text”:A2.(NAME),”axis1″:”x”,”data1″:A2.(NAME),”axis2″:”y”,”data2″:A2.(SCORE)). By doing so, the appearance properties will be changed as follows:
Set the color for border line as turquoise and the weight as 1, and specify a sequence of fill colors for the sectors. Thus the plotting result is:
As we can see, the appearance of the pie chart has changed. The default lighting effects of the fill colors have vanished and the gradient color has been applied to the entire circle area to achieve harmony of the fill colors.
And, the pie chart’s data labels, different from those in other styles of charts, are presented by lines drew from the center of each sector. So we need to specify the appearance properties for these guide lines as well, besides those for data label texts. Modify the sector element’s plotting properties by editing A6’s code:
Then the plotting result is:
Now we’ll see the text properties. The above plotting algorithm sets the data labels as names of the athletes. Modify A6 to change the plotting properties of the sector element:
Here we modify the text font, text style, text size and text color for the data label texts, and the plotting result is:
It can be seen that the text properties apply in both the texts on the pie and those using guide lines.
3. Pie charts with series and categories
Similar to a stacked column chart, a pie chart can display data series and data categories at the same time. Yet they have differences. In a pie chart with both series and categories, the plotting results corresponding to data categries accumulate to form a ring or a circle, which represents the percentage of a certain category. Below is the plotting algorithm of a pie chart for showing results of different gym events. For the convenience of observation, A7 adds legends to the chart:
|2||=demo.query(“select * from GYMSCORE order by NAME,EVENT”)|
Here we still use an enumeration axis as polar axis x and a numeric axis as radial axis y. A6 specifies data properties for the sector element. Note that Data1 includes both NAME values of series data and EVENT values of category data.
A8’s plotting result is:
So, in a pie chart with both series and categories, polar axis data should contain category and series at the same time. Based on data of categories, a circle or a ring will be plotted, with data labels being presented using guide lines changing to series.
By default we’ll plot a pie chart displaying percentage values with the sector element. We can only read the percentage of each event for each athlete. Modify the stack type property in A6:
Here Stack type property is changed from the default Stacked by percent to Stacked by value. Thus data in each category will be accumulated by statistical values, producing the following plotting result:
As can be seen, accumulated by values, the slices for all athletes will be plotted based on their scores and thus the plotting result for each category will not be a complete circle or a complete ring any more. As with a stacked column chart, we can see the total scores of each of the athletes through this type of pie chart.