Report

Introduction to Lattice Graphics Richard Pugh 4th 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 • 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 Overview of Lattice Graphics 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 List of Lattice Graphic Functions Function xyplot histogram densityplot barchart bwplot qq dotplot cloud wireframe splom parallel Description Scatter plot Univariate histogram Univariate density line plot Bar chart Box and whisker plot Normal QQ plot Label dot plot 3D scatter plot 3D surface plot Scatter matrix plot Multivariate parallel plot Graph Type Bivariate Univariate Univariate Univariate Bivariate Univariate Bivariate 3D 3D Data Frame Data Frame Key Function Arguments Argument x data subset panel groups Type of graph Univariate Bivariate 3D Data Frame Description Plot definition, typically as a formula The data frame used for the graphic Any subsets to be applied to the data Function used to draw data in each “panel” Grouping variable for the plot Formula ~Y Y~X Z ~ X*Y ~ Data Y axis Y Y Y Data X axis X X - Z axis Z - Creating Basic Graphics Panelled Graphics 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 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 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 Grouped Data 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 Take care! 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 Multiple Variables 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 Writing Panel Functions 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 … Panel Functions • The default “panel” function for a lattice function is “panel.NameOfFunction” • Let’s look at panel.xyplot … Arguments for styling Jitter & other less used bits Let’s write our own panel function ……. 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 Summary 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 …