RadarChartTableDataModel: Basic Charts

The main responsibility of a RadarChartTableDataModel is to determine which data variables are used in the radar chart and what role each variable plays. The primary roles are

CategoryVariable

Specifies a classification variable whose values determine the number and arrangement of spokes (axis lines) in the chart. One spoke is produced for each unique classification value or combination of values when other variable roles are specified. Because a radar chart needs to organize the category variable's data values into groups (typically called bins), the CategoryVariable role uses a ClassificationVariable, which is designed to manage and sort categorical values. nVariable is designed to manage and sort categorical groupings.

ResponseVariable

Specifies an analysis variable whose values represent the values of the chart statistic for the data categories and therefore determine the length of the vertices along the spokes. The role uses an AnalysisVariable so it can associate a statistical computation with the response variable.

The following code fragment graphs the causes of failure for different cleaning processes that were used by two manufacturing systems. The code assigns the Category and Response variable roles to data columns named Cause and Count:

 
// Create a data source that must contain a string column
// named Cause and a numeric column named Count
   javax.swing.table.TableModel dataTable = <...>;

// Create a data model and attach the data source to it
   RadarChartTableDataModel dataModel=
        new RadarChartTableDataModel();
   dataModel.setModel(dataTable);
     
// Assign the Category and Response variable roles
// to appropriate variable(s)
   dataModel.setCategoryVariable(
     new ClassificationVariable("Cause"));
   dataModel.setResponseVariable(
     new AnalysisVariable("Count"));

// Create a RadarChart and attach the data model to it
   RadarChart radarChart = new RadarChart();
   radarChart.setDataModel(dataModel);

RadarChartTableDataModel: Data Summarization and Statistic Calculation

When a data model is assigned to a RadarChart, the chart summarizes the data before displaying it. During summarization

• Analysis values are grouped into bins that are arranged by the classification values. For example, if the classification values represent sales territories, each bin represents one of the territories, and there is a bin for each territory.
• The statistic (set by the analysis variable's constructor) is applied to the analysis values in each bin. For example, if the analysis values represent contamination measures in a manufacturing process and the statistic is Sum, then the contamination measures in each bin are totaled.
• The RadarChart displays the results for each bin as a point representing the computed statistic value on a chart spoke.

The following statistics are the default calculations:

• If a response variable is not specified, a FREQUENCY count is calculated for each category value.
• If a response variable is specified but no statistic is specified, a SUM is calculated for the response values associated with each category value.

The AnalysisVariable constructor can be used to specify a statistic to calcuate. Valid statistics to calculate are a frequency count, a sum, or a mean. The following code fragment specifies a mean:

 
AnalysisVariable response=new AnalysisVariable(
  "Var1"                            // column for Response role
  ,GraphConstants.STATISTIC_MEAN    // statistic to calculate
);
RadarChartTableDataModel dataModel=new RadarChartTableDataModel();
dataModel.setResponseVariable(response);

RadarChartTableDataModel: Data Subgroups

To identify data subgroups according to the values of a ClassificationVariable, assign the SubroupVariable role to the appropriate classification variable. The chart generates a separate star for each value of the Subgroup variable. All stars are overlapped on the same set of spokes.

For example, if a chart represents the causes of failure for two different cleaning processes in a manufacturing system, a variable named Process might be assigned the Subgroup role to identify each process. The Subgroup role would cause a separate star to be generated for each process. The assignment would resemble the following:

 
RadarChartTableDataModel dataModel=
  new RadarChartTableDataModel();
dataModel.setSubgroupVariable(new ClassificationVariable("Process"));

Different colored area fills are used to represent each unique value of the Subgroup variable. To turn off the area fills, get the chart's RadarChartModel and call the model's setFilledRadar() method with the argument value false, as in

radarChart.getGraphModel().setFilledRadar(false);

RadarChartTableDataModel: Multiple Charts in Columns and/or Rows

Separate RadarCharts can be generated for each value of a ClassificationVariable by assigning either the ColumnVariable or RowVariable role to that variable.

For example, when charting the causes of failure for two different cleaning processes in a manufacturing system, a variable named Process might be assigned the Column role so that a separate chart is generated for each process. The assignment would resemble the following:

 
RadarChartTableDataModel dataModel=
  new RadarChartTableDataModel();
dataModel.setColumnVariable(new ClassificationVariable("Process"));

If the Column role is assigned, charts are aligned horizontally by the specified variable's values. If the Row role is assigned, charts are aligned vertically by the variable's values. In either case, each chart has its own axes.

The Column and Row variable roles can both be assigned to the same graph. In that case, a separate radar chart is produced for each unique pair of (column, row) values, and the charts are displayed in a grid. For example, when charting the causes of failure for two cleaning processes used in a manufacturing system, a variable named Day might be assigned the Column role and a variable named Process might be assigned the Row role. In this case, a separate chart is generated for each process's failures on each day.

RadarChartTableDataModel: Valid Variable Roles

The following table summarizes the RadarChartTableDataModel variable roles and the type of data each role supports.

Variable Role	Class Type	Numeric	String	Multiple Variables
CategoryVariable* Assigns the variable whose values determine the number and arrangement of spokes in the radar chart.	ClassificationVariable	Yes	Yes	Yes
ResponseVariable Assigns the variable whose values are used to calculate the chart statistic and therefore determine the lenth of the spokes	AnalysisVariable	Yes	No	Yes
SubgroupVariable Generates a separate star for each subgroup value, and the stars are overlapped on the same set of spokes	ClassificationVariable	No	Yes	No
ColumnVariable Generates a separate radar chart for each value of the specified variable and aligns the multiple charts in columns	ClassificationVariable	Yes	Yes	Yes
RowVariable Generates a separate radar chart for each value of the specified variable and aligns the multiple charts in rows	ClassificationVariable	Yes	Yes	Yes
* required variable

RadarChartTableDataModel: Behavior

To generate a graph, a RadarChart needs a data column for the CategoryVariable role. If the Category role is not assigned in the program code, a RadarChart selects the first string column found in the RadarChartTableDataModel and uses it as its Category variable. If there is no string column in the data, then it selects the first numeric column.

This default behavior occurs only when the Category role is not assigned. If the role is assigned to a variable that does not exist in the data, the RadarChart cannot display a graph.

If the ResponseVariable role is not assigned in the program code, then the lengths of the spoke vertices represent a frequency count of the Category values. If the ResponseVariable role is assigned, then the default statistic for the spoke vertices is the sum of the response values for each category value.

RadarChartTableDataModel: Events

A RadarChartTableDataModel fires property change events when

• any of its properties are changed
• any property in a contained model is modified.

For example, if the name property is changed in the ClassificationVariable that has been assigned the CategoryVariable role, the RadarChartTableDataModel fires a ProeprtyChangeEvent stating that the CategoryVariable has changed.

RadarChartTableDataModel: Error Handling

When variable roles are assigned, the RadarChartTableDataModel does not confirm that the variables exist in the TableModel. Thus, assigning a non-existent data column to a variable role may mean that the RadarChart cannot display a graph. For example, if the CategoryVariable role is assigned to a Cause column but the TableModel does not contain a Cause column, then the RadarChart fails to produce a graph.

If the CategoryVariable role is correctly assiged to an existing variable but another role is incorrectly assigned, the RadarChart displays a graph without the incorrect role. For example, if the CategoryVariable role is correctly assigned but the ColumnVariable role is not, a graph using the Category role is generated, but the Column role is ignored.