The Convex Hulls Options page of the format graph dialog allows you to add and customize these data objects on graphs with the appropriate data structure.

Required data structure

In order to be able to enable convex hulls on your graph, a continuous variable must be assigned to both the X (horizontal) and Y (vertical) axes. This data object will not be available if categorical variables are assigned to these axes, or if the “Rows” and “Columns” options have been selected. In these cases, the following message will be displayed in the Format Graph dialog for this data object:

“The Convex hulls data object cannot be added to this graph because it is incompatible with the current axis variable assignments. Switch to the Axis Variables tab of this dialog to update these assignments.”

Format Options

The checkbox at the top of the options page will allow you to toggle on or off convex hulls on the graph. On macOS, this is a toggle as opposed to a checkbox.

Once enabled, you will be able to specify how the data should be grouped in order to generate convex hulls. The options here are:

•One for all data

•One for each group defined by a categorical grouping variable

Note that the selection that you make will determine the available options for both Fill Color and Border options of the convex hulls.

One for all data

This option will consider all of the data on the graph as a single group, and will generate a convex hull using information from all values to calculate the size, shape, and position of the hull.

One for each group defined by a categorical variable

This option will require that you select a categorical grouping variable from the input data. The levels of this categorical variable will be used to assign rows of data to different groups, and a separate convex hull will be generated for each group. Only the data assigned to a given group will be used when calculating the size, shape, and position of the convex hull for that group.

Fill Color Options

There are three primary options to choose from when defining the fill color of convex hulls on your graphs:

•None (no fill color for any convex hulls)

•Single color (for all convex hulls)

•Variable (by group)

The first two of these options are rather self explanatory. If you choose “No fill”, then none of the convex hulls on your graph will have any fill color applied. If you choose “Single color”, then you will be able to select a fill color and transparency level. These color and transparency settings will be applied to all convex hulls on your graph.

If you chose the option “one [convex hull] for all data” when specifying how many convex hulls to generate, then these are the only two options that will be available to you. Because there will only be one convex hull, there’s no need to specify multiple different fill colors!

However, multiple convex hulls can be generated for a single graph by selecting the option “one for each group defined by:” and specifying a categorical variable to serve as a grouping variable. One convex hull will be generated from the data for each group defined by that grouping variable. If you chose this option, then you will also be able to select the “Variable (by group)” option for the fill color of the resulting convex hulls. When using this option, you may choose a color scheme to apply to the convex hull fill colors, or you may choose a specific group to specify its fill color and transparency.

Border Options

There are three primary options to choose from when defining the border options of convex hulls on your graphs:

•None (no border for any convex hulls)

•Single color (for all convex hulls)

•Variable (by group)

The first two of these options are rather self explanatory. If you choose “None”, then none of the convex hulls on your graph will have any border displayed. If you choose “Single color”, then you will be able to select a border color, transparency level, thickness, and line style. These visual settings will be applied to the borders of all convex hulls on your graph.

If you chose the option “one [convex hull] for all data” when specifying how many convex hulls to generate, then these are the only two options that will be available to you. Because there will only be one convex hull, there’s no need to specify multiple different sets of border options!

However, multiple convex hulls can be generated for a single graph by selecting the option “one for each group defined by:” and specifying a categorical variable to serve as a grouping variable. One convex hull will be generated from the data for each group defined by that grouping variable. If you chose this option, then you will also be able to select the “Variable (by group)” option for the border options of the resulting convex hulls. When using this option, you may choose a color scheme to apply to the convex hull border colors, or you may choose a specific group to specify its fill color. For each group, you may also specify different options for border transparency, thickness, and line style. Alternatively, you may use the “Global” dropdown to select multiple groups or all groups at once when specifying these formatting options.