Introduction to Trellis Graphics
Trellis graphs allow you to view relationships between different variables in your data set through conditioning.
Suppose you have a data set based on multiple variables and you want to see how plots of two variables change with variations in a third "conditioning" variable. By using Trellis graphics you can view your data in a series of panels where each panel contains a subset of the original data divided into intervals of the conditioning variable.
For example, a data set contains information on the high school graduation rate per year and average income per household per year for all 50 states. You could plot income against graduation for different regions of the USA, for instance, South, North, East and West to determine if the relationship varies geographically. In this case, the regions of the USA would be the conditioning variable.
|
A Trellis graph. |
In S-PLUS, all graphs can be conditioned using Trellis graphics. The data columns used for the plot and for the conditioning variables must be of equal length. The axis specifications and panel display attributes (for example, fill color) are identical for each panel, although axis ranges may be allowed to vary. The border and fill attributes for the panels can be specified on the Fill/Border page of the Graph Properties dialog.