1. Introduction to
Lattice Graphics
Richard Pugh
4th December 2012

2. Agenda Overview of Lattice Functions Creating basic graphics
Panelled Graphics
Grouped Data
Multiple Variables
Writing Panel Functions
Summary

3. The Data We Will Use
Something relevant and sector independent
London Tube Performance Data from the TFL website
Excess Travel Hours by Line

5. Overview of Lattice Graphics

6. Overview of Lattice Graphics
One of the graphic systems of R (others include “Traditional” and “GGPlot”)
An implementation of the S+ “Trellis” Graphics
Written by Deepayan Sarkar, Fred Hutchinson Cancer Research Center

7. List of Lattice Graphic Functions
Description
Graph Type
xyplot
Scatter plot
Bivariate
histogram
Univariate histogram
Univariate
densityplot
Univariate density line plot
barchart
Bar chart
bwplot
Box and whisker plot qq
Normal QQ plot
dotplot
Label dot plot
cloud
3D scatter plot 3D
wireframe
3D surface plot
splom
Scatter matrix plot
Data Frame
parallel
Multivariate parallel plot

8. Key Function Arguments
Description x
Plot definition, typically as a formula
data
The data frame used for the graphic
subset
Any subsets to be applied to the data
panel
Function used to draw data in each “panel”
groups
Grouping variable for the plot
Type of graph
Formula
Y axis
X axis
Z axis
Univariate
~ Y Y -
Bivariate
Y ~ X X 3D
Z ~ X*Y Z
Data Frame
~ Data
Data

9. Creating Basic Graphics

16. Panelled Graphics

17. Specifying Panels
We can use the vertical pipe symbol “|” in order to specify “panels” to be plotted
This allows us to create the graphics “by” one or more variables

22. Panel Variables
During the plot creation, lattice builds a plot data frame containing the variables to plot
By this time, any categorical “by” variables need to be factors
So, either change them to characters or factors beforehand

25. Panel Ordering!
If you have a factor variable, the ordering of the panels is in “graph” and not “table” order (!!)
We can resolve using as.table = TRUE
Note that the converting of characters to factors uses alphabetical ordering

29. Grouped Data

30. Grouped Data
We can specify groupings within our data in order to plot these groupings separately
By default, lattice will vary styling of the groups specified
The key argument is the “groups” argument

31. Take care!

33. Controlling Styles
Best done via the underlying lattice style templates
Use of par.settings argument which takes a list of styles
We usually use a basic template and change elements of it
The show.settings function lets you see the current (or adapted) styles

38. Multiple Variables

39. Multiple Variables
We can specify one or more X or Y axis variable in our lattice formula
This can overwrite the “groups” input
The “outer” argument controls how the multiple X/Y variables should be plotted

45. Writing Panel Functions

46. Panel Functions
For each lattice graph, R performs the following actions:
Partitions the data
Draws the graph “outline” (i.e. the “panels”)
Passes the data for each panel into the “panel” function
We can overwrite this panel function and supply our own …

47. Panel Functions
The default “panel” function for a lattice function is “panel.NameOfFunction”
Let’s look at panel.xyplot …

48. Arguments for styling
Jitter & other less used bits
Let’s write our own panel function …….

52. Now what?
Now we can insert other functions into a panel function which will then impact each individual plot panel
We can call:
Lattice “low level functions” (lpoints, ltext, llines, lpolygon etc)
Existing “panel.” functions that exist for this purpose

55. Summary

56. Summary This was just a quick overview of lattice graphics
I hope it was useful
For more info, look in the Lattice book, find examples online or contact Mango …