Wildcards let you to precisely vary the properties of a specification to generate multiple visualizations in parallel. There are three types of wildcards: Wildcard Fields, Wildcard Shelves and Wildcard functions.
Wildcard fields let you create multiple views in parallel by enumerating over a set of fields. Quantitative, Categorical, and Temporal field wildcards are provided by default, though you can manually author custom wildcards containing the desired fields.
Preset Wildcard Fields
These wildcards represent all fields of a particular data type (Quantitative, Categorical, and Temporal). You can simply drag-and-drop a wildcard field onto an encoding shelf to create multiple charts in parallel.
Custom Wildcard Fields
To create a wildcard for a specific set of fields, you can author a custom wildcard field by dragging desired fields to the wildcard list. However, to avoid incongruous views, you are prevented from creating custom wildcard fields that contain multiple data types.
Wildcard shelves let you add fields without selecting a specific channel, allowing the system to suggest appropriate encodings.
The screenshot below shows the system automatically encoding the two quantitative fields onto the x and y channels since they were the most perceptually effective and expressive channels available.
Wildcard functions allow simultaneous specification of data field transformations. When the Wildcard button is checked, the radio buttons for each function will become check-boxes, allowing you to select the functions you want to enumerate. The field pill will denote that it has become a wildcard field by wrapping the field name with with “?”.