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Introduction to Lattice Graphics

Introduction to Lattice Graphics. Richard Pugh 4 th December 2012. Agenda. Overview of Lattice Functions Creating basic graphics Panelled Graphics Grouped Data Multiple Variables Writing Panel Functions Summary. The Data We Will Use. Something relevant and sector independent

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Introduction to Lattice Graphics

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  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 http://data.london.gov.uk/datastore/package/tube-network-performance-data http://en.wikipedia.org/wiki/London_Underground

  4. Overview of Lattice Graphics

  5. 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 DeepayanSarkar, Fred Hutchinson Cancer Research Center

  6. List of Lattice Graphic Functions

  7. Key Function Arguments

  8. Creating Basic Graphics

  9. Panelled Graphics

  10. 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

  11. 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

  12. 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

  13. Grouped Data

  14. 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

  15. Take care!

  16. 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

  17. Multiple Variables

  18. 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

  19. Writing Panel Functions

  20. 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 …

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

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

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