Pie and serial charts both support having a selection made on them; that is, they support a selection-change event. This means that they can be configured as the source of an action. To understand how chart selection works, a review of their building blocks provides more context.
A chart is a graphical representation of one or more series of data points. Think of a series as an array, and each data point in the array is a name-value pair.
A serial chart can have more than one series, whereas a pie chart has only one. In many chart configurations, it is incorrect to equate a data point with a row or feature of data from your data source. For example, the information on a chart can represent rows that have been grouped on a common attribute and to which a summary statistic has been applied. Similarly, the data may be date based, and the input rows have been grouped or binned to a common unit of time before being displayed on the chart. For these reasons, you need to think of the data you see on a chart in terms of data points.
Every data point rendered on a chart has a shape: rectangle (bar), circular sector (pie slice), or point (with straight or smoother line segments connecting the points).
On a serial chart, the data represented can have discrete or continuous categories (dates). Discrete categories represent unique values, whereas continuous categories represent a time range.
A chart selection represents one or more data points. The selected data points are brought to the forefront by being rendered opaque. All unselected data points are pushed to the background by being rendered semitransparent.
At run time, chart selections are only enabled if the chart has an action configured. This means that when a chart's selection changes, one or more targets can be affected (for example, another dashboard element, a selector, a map, or a map's operational layer).
The way you configure a chart determines the actions that can be configured.
|Configuration option||Possible action|
Categories from Grouped Values
Categories from Features
Categories from Fields
Not applicable (selection is not possible)
In the case of the Filter action, only elements that are based on the same underlying data source can be used as targets.
Charts support two selection modes: single and multiple. When configured for multiple selection, a selection can be created by clicking many data points, or the user can drag across an area of the chart.
- When showing continuous categories such as date-based data, each selected data point represents a range of time. The size of the range is determined by the minimum period on the chart's configuration.
- When showing discrete categories—that is, not date based—a serial chart's category axis label can be used to create a selection. This is particularly useful on multiseries charts.
- Clicking a data point selects it. Clicking it again deselects it.
- Clicking anywhere that does not represent a data point on a chart clears the selection.
- Some charts have legends displayed. Clicking the legend removes the related data points from the chart. If those points happen to be selected when the legend is clicked, clicking the legend again does not reselect the affected data points.